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 $208.79   6.316%   $221.9772   $221.98   $222.00   $222.00  
  Purchase #2 $116.55   11.203%   $129.6071   $129.61   $129.60   $129.60  
  Purchase #3 $156.49   12.221%   $175.6146   $175.61   $175.60   $175.60  
  Purchase #4 $62.63   9.125%   $68.345   $68.35   $68.35   $68.30  
  Purchase #5 $225.46   6.559%   $240.2479   $240.25   $240.25   $240.20  
  Purchase #6 $94.33   10.602%   $104.3309   $104.33   $104.35   $104.30  
  Purchase #7 $19.31   12.682%   $21.7589   $21.76   $21.75   $21.80  
  7 purchase totals = $883.56       $961.8816   $961.89   $961.90   $961.80