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 $82.91   12.577%   $93.3376   $93.34   $93.35   $93.30  
  Purchase #2 $188.86   8.771%   $205.4249   $205.42   $205.40   $205.40  
  Purchase #3 $151.93   5.507%   $160.2968   $160.30   $160.30   $160.30  
  Purchase #4 $121.51   5.576%   $128.2854   $128.29   $128.30   $128.30  
  Purchase #5 $116.26   4.329%   $121.2929   $121.29   $121.30   $121.30  
  Purchase #6 $9.27   10.301%   $10.2249   $10.22   $10.20   $10.20  
  Purchase #7 $234.89   9.715%   $257.7096   $257.71   $257.70   $257.70  
  7 purchase totals = $905.63       $976.5721   $976.57   $976.55   $976.50