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 $54.67   6.335%   $58.1333   $58.13   $58.15   $58.10  
  Purchase #2 $126.42   8.269%   $136.8737   $136.87   $136.85   $136.90  
  Purchase #3 $110.68   9.781%   $121.5056   $121.51   $121.50   $121.50  
  Purchase #4 $236.61   5.854%   $250.4611   $250.46   $250.45   $250.50  
  Purchase #5 $132.54   3.311%   $136.9284   $136.93   $136.95   $136.90  
  Purchase #6 $72.87   13.406%   $82.639   $82.64   $82.65   $82.60  
  Purchase #7 $207.78   8.584%   $225.6158   $225.62   $225.60   $225.60  
  7 purchase totals = $941.57       $1,012.1569   $1,012.16   $1,012.15   $1,012.10