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 $51.79   12.575%   $58.3026   $58.30   $58.30   $58.30  
  Purchase #2 $120.83   11.747%   $135.0239   $135.02   $135.00   $135.00  
  Purchase #3 $214.92   10.147%   $236.7279   $236.73   $236.75   $236.70  
  Purchase #4 $195.85   12.787%   $220.8933   $220.89   $220.90   $220.90  
  Purchase #5 $228.74   10.771%   $253.3776   $253.38   $253.40   $253.40  
  Purchase #6 $162.30   12.386%   $182.4025   $182.40   $182.40   $182.40  
  Purchase #7 $60.38   11.240%   $67.1667   $67.17   $67.15   $67.20  
  7 purchase totals = $1,034.81       $1,153.8945   $1,153.89   $1,153.90   $1,153.90