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 $87.47   10.196%   $96.3884   $96.39   $96.40   $96.40  
  Purchase #2 $6.71   8.240%   $7.2629   $7.26   $7.25   $7.30  
  Purchase #3 $15.76   9.166%   $17.2046   $17.20   $17.20   $17.20  
  Purchase #4 $106.91   5.641%   $112.9408   $112.94   $112.95   $112.90  
  Purchase #5 $221.92   9.146%   $242.2168   $242.22   $242.20   $242.20  
  Purchase #6 $193.52   9.381%   $211.6741   $211.67   $211.65   $211.70  
  Purchase #7 $59.46   5.328%   $62.628   $62.63   $62.65   $62.60  
  7 purchase totals = $691.75       $750.3156   $750.31   $750.30   $750.30