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 $195.96   5.144%   $206.0402   $206.04   $206.05   $206.00  
  Purchase #2 $68.57   13.328%   $77.709   $77.71   $77.70   $77.70  
  Purchase #3 $139.96   8.869%   $152.3731   $152.37   $152.35   $152.40  
  Purchase #4 $89.89   13.742%   $102.2427   $102.24   $102.25   $102.20  
  Purchase #5 $132.86   11.244%   $147.7988   $147.80   $147.80   $147.80  
  Purchase #6 $37.97   7.340%   $40.757   $40.76   $40.75   $40.80  
  Purchase #7 $215.79   6.494%   $229.8034   $229.80   $229.80   $229.80  
  7 purchase totals = $881.00       $956.7242   $956.72   $956.70   $956.70