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 $54.27   8.330%   $58.7907   $58.79   $58.80   $58.80  
  Purchase #2 $187.41   7.659%   $201.7637   $201.76   $201.75   $201.80  
  Purchase #3 $122.89   4.476%   $128.3906   $128.39   $128.40   $128.40  
  Purchase #4 $148.81   5.725%   $157.3294   $157.33   $157.35   $157.30  
  Purchase #5 $141.84   3.795%   $147.2228   $147.22   $147.20   $147.20  
  Purchase #6 $60.33   10.855%   $66.8788   $66.88   $66.90   $66.90  
  Purchase #7 $61.49   7.284%   $65.9689   $65.97   $65.95   $66.00  
  7 purchase totals = $777.04       $826.3449   $826.34   $826.35   $826.40