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 $207.96   12.513%   $233.982   $233.98   $234.00   $234.00  
  Purchase #2 $9.26   13.171%   $10.4796   $10.48   $10.50   $10.50  
  Purchase #3 $68.95   6.466%   $73.4083   $73.41   $73.40   $73.40  
  Purchase #4 $87.39   11.464%   $97.4084   $97.41   $97.40   $97.40  
  Purchase #5 $246.52   8.865%   $268.374   $268.37   $268.35   $268.40  
  Purchase #6 $176.43   9.155%   $192.5822   $192.58   $192.60   $192.60  
  Purchase #7 $22.33   6.249%   $23.7254   $23.73   $23.75   $23.70  
  7 purchase totals = $818.84       $899.9599   $899.96   $900.00   $900.00