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 $219.53   7.355%   $235.6764   $235.68   $235.70   $235.70  
  Purchase #2 $65.56   5.137%   $68.9278   $68.93   $68.95   $68.90  
  Purchase #3 $188.46   6.827%   $201.3262   $201.33   $201.35   $201.30  
  Purchase #4 $58.58   13.724%   $66.6195   $66.62   $66.60   $66.60  
  Purchase #5 $121.55   6.754%   $129.7595   $129.76   $129.75   $129.80  
  Purchase #6 $219.65   11.528%   $244.9713   $244.97   $244.95   $245.00  
  Purchase #7 $11.65   4.657%   $12.1925   $12.19   $12.20   $12.20  
  7 purchase totals = $884.98       $959.4732   $959.48   $959.50   $959.50