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 $217.63   13.453%   $246.9078   $246.91   $246.90   $246.90  
  Purchase #2 $116.88   4.330%   $121.9409   $121.94   $121.95   $121.90  
  Purchase #3 $121.70   9.102%   $132.7771   $132.78   $132.80   $132.80  
  Purchase #4 $36.31   11.715%   $40.5637   $40.56   $40.55   $40.60  
  Purchase #5 $93.95   5.173%   $98.81   $98.81   $98.80   $98.80  
  Purchase #6 $148.32   9.102%   $161.8201   $161.82   $161.80   $161.80  
  Purchase #7 $188.76   7.329%   $202.5942   $202.59   $202.60   $202.60  
  7 purchase totals = $923.55       $1,005.4138   $1,005.41   $1,005.40   $1,005.40