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 $82.72   13.208%   $93.6457   $93.65   $93.65   $93.60  
  Purchase #2 $135.82   11.687%   $151.6933   $151.69   $151.70   $151.70  
  Purchase #3 $197.75   11.427%   $220.3469   $220.35   $220.35   $220.30  
  Purchase #4 $74.85   5.269%   $78.7938   $78.79   $78.80   $78.80  
  Purchase #5 $35.80   9.689%   $39.2687   $39.27   $39.25   $39.30  
  Purchase #6 $187.43   9.674%   $205.562   $205.56   $205.55   $205.60  
  Purchase #7 $127.75   6.765%   $136.3923   $136.39   $136.40   $136.40  
  7 purchase totals = $842.12       $925.7027   $925.70   $925.70   $925.70