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 $84.81   10.361%   $93.5972   $93.60   $93.60   $93.60  
  Purchase #2 $65.52   10.146%   $72.1677   $72.17   $72.15   $72.20  
  Purchase #3 $17.46   10.184%   $19.2381   $19.24   $19.25   $19.20  
  Purchase #4 $241.64   4.166%   $251.7067   $251.71   $251.70   $251.70  
  Purchase #5 $98.64   6.401%   $104.9539   $104.95   $104.95   $105.00  
  Purchase #6 $139.86   7.598%   $150.4866   $150.49   $150.50   $150.50  
  Purchase #7 $215.37   10.644%   $238.294   $238.29   $238.30   $238.30  
  7 purchase totals = $863.30       $930.4442   $930.45   $930.45   $930.50