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 $211.83   9.865%   $232.727   $232.73   $232.75   $232.70  
  Purchase #2 $42.75   7.552%   $45.9785   $45.98   $46.00   $46.00  
  Purchase #3 $219.96   7.686%   $236.8661   $236.87   $236.85   $236.90  
  Purchase #4 $200.40   10.227%   $220.8949   $220.89   $220.90   $220.90  
  Purchase #5 $56.99   9.641%   $62.4844   $62.48   $62.50   $62.50  
  Purchase #6 $18.71   4.428%   $19.5385   $19.54   $19.55   $19.50  
  Purchase #7 $238.58   12.486%   $268.3691   $268.37   $268.35   $268.40  
  7 purchase totals = $989.22       $1,086.8585   $1,086.86   $1,086.90   $1,086.90