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 $190.67   8.706%   $207.2697   $207.27   $207.25   $207.30  
  Purchase #2 $211.99   11.650%   $236.6868   $236.69   $236.70   $236.70  
  Purchase #3 $161.91   12.695%   $182.4645   $182.46   $182.45   $182.50  
  Purchase #4 $47.26   11.589%   $52.737   $52.74   $52.75   $52.70  
  Purchase #5 $34.47   4.316%   $35.9577   $35.96   $35.95   $36.00  
  Purchase #6 $99.68   10.636%   $110.282   $110.28   $110.30   $110.30  
  Purchase #7 $208.75   3.815%   $216.7138   $216.71   $216.70   $216.70  
  7 purchase totals = $954.73       $1,042.1115   $1,042.11   $1,042.10   $1,042.20