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 $63.57   4.664%   $66.5349   $66.53   $66.55   $66.50  
  Purchase #2 $105.93   9.695%   $116.1999   $116.20   $116.20   $116.20  
  Purchase #3 $108.79   10.477%   $120.1879   $120.19   $120.20   $120.20  
  Purchase #4 $157.73   11.357%   $175.6434   $175.64   $175.65   $175.60  
  Purchase #5 $237.39   13.267%   $268.8845   $268.88   $268.90   $268.90  
  Purchase #6 $110.38   6.111%   $117.1253   $117.13   $117.15   $117.10  
  Purchase #7 $129.37   6.685%   $138.0184   $138.02   $138.00   $138.00  
  7 purchase totals = $913.16       $1,002.5943   $1,002.59   $1,002.65   $1,002.50