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 $180.89   8.869%   $196.9331   $196.93   $196.95   $196.90  
  Purchase #2 $126.95   8.153%   $137.3002   $137.30   $137.30   $137.30  
  Purchase #3 $36.47   11.113%   $40.5229   $40.52   $40.50   $40.50  
  Purchase #4 $101.43   13.820%   $115.4476   $115.45   $115.45   $115.40  
  Purchase #5 $181.66   6.358%   $193.2099   $193.21   $193.20   $193.20  
  Purchase #6 $243.81   10.507%   $269.4271   $269.43   $269.45   $269.40  
  Purchase #7 $65.74   6.280%   $69.8685   $69.87   $69.85   $69.90  
  7 purchase totals = $936.95       $1,022.7093   $1,022.71   $1,022.70   $1,022.60