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 $194.69   3.417%   $201.3426   $201.34   $201.35   $201.30  
  Purchase #2 $47.57   5.152%   $50.0208   $50.02   $50.00   $50.00  
  Purchase #3 $53.45   4.238%   $55.7152   $55.72   $55.70   $55.70  
  Purchase #4 $233.61   12.621%   $263.0939   $263.09   $263.10   $263.10  
  Purchase #5 $115.28   11.242%   $128.2398   $128.24   $128.25   $128.20  
  Purchase #6 $87.95   4.678%   $92.0643   $92.06   $92.05   $92.10  
  Purchase #7 $68.87   11.822%   $77.0118   $77.01   $77.00   $77.00  
  7 purchase totals = $801.42       $867.4884   $867.48   $867.45   $867.40