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 $48.92   11.134%   $54.3668   $54.37   $54.35   $54.40  
  Purchase #2 $116.92   5.775%   $123.6721   $123.67   $123.65   $123.70  
  Purchase #3 $72.47   3.481%   $74.9927   $74.99   $75.00   $75.00  
  Purchase #4 $149.79   8.778%   $162.9386   $162.94   $162.95   $162.90  
  Purchase #5 $65.61   3.665%   $68.0146   $68.01   $68.00   $68.00  
  Purchase #6 $225.74   13.667%   $256.5919   $256.59   $256.60   $256.60  
  Purchase #7 $170.33   12.868%   $192.2481   $192.25   $192.25   $192.20  
  7 purchase totals = $849.78       $932.8248   $932.82   $932.80   $932.80