Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $178.90   12.777%   $201.7581   $201.76   $201.75   $201.80  
  Purchase #2 $181.36   11.523%   $202.2581   $202.26   $202.25   $202.30  
  Purchase #3 $119.46   11.244%   $132.8921   $132.89   $132.90   $132.90  
  Purchase #4 $188.34   5.508%   $198.7138   $198.71   $198.70   $198.70  
  Purchase #5 $153.52   12.361%   $172.4966   $172.50   $172.50   $172.50  
  Purchase #6 $129.53   10.226%   $142.7757   $142.78   $142.80   $142.80  
  Purchase #7 $157.98   11.415%   $176.0134   $176.01   $176.00   $176.00  
  7 purchase totals = $1,109.09       $1,226.9078   $1,226.91   $1,226.90   $1,227.00