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 $64.63   13.615%   $73.4294   $73.43   $73.45   $73.40  
  Purchase #2 $53.65   6.379%   $57.0723   $57.07   $57.05   $57.10  
  Purchase #3 $93.59   8.238%   $101.2999   $101.30   $101.30   $101.30  
  Purchase #4 $58.79   12.828%   $66.3316   $66.33   $66.35   $66.30  
  Purchase #5 $242.66   8.465%   $263.2012   $263.20   $263.20   $263.20  
  Purchase #6 $133.95   3.670%   $138.866   $138.87   $138.85   $138.90  
  Purchase #7 $247.92   5.186%   $260.7771   $260.78   $260.80   $260.80  
  7 purchase totals = $895.19       $960.9775   $960.98   $961.00   $961.00