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 $47.75   3.592%   $49.4652   $49.47   $49.45   $49.50  
  Purchase #2 $188.73   6.853%   $201.6637   $201.66   $201.65   $201.70  
  Purchase #3 $242.69   12.517%   $273.0675   $273.07   $273.05   $273.10  
  Purchase #4 $25.67   4.702%   $26.877   $26.88   $26.90   $26.90  
  Purchase #5 $13.93   11.550%   $15.5389   $15.54   $15.55   $15.50  
  Purchase #6 $161.96   12.596%   $182.3605   $182.36   $182.35   $182.40  
  Purchase #7 $21.88   3.502%   $22.6462   $22.65   $22.65   $22.60  
  7 purchase totals = $702.61       $771.6190   $771.63   $771.60   $771.70