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 $94.98   13.372%   $107.6807   $107.68   $107.70   $107.70  
  Purchase #2 $236.30   9.590%   $258.9612   $258.96   $258.95   $259.00  
  Purchase #3 $32.71   8.448%   $35.4733   $35.47   $35.45   $35.50  
  Purchase #4 $49.61   10.276%   $54.7079   $54.71   $54.70   $54.70  
  Purchase #5 $123.91   8.417%   $134.3395   $134.34   $134.35   $134.30  
  Purchase #6 $131.28   3.455%   $135.8157   $135.82   $135.80   $135.80  
  Purchase #7 $28.86   13.534%   $32.7659   $32.77   $32.75   $32.80  
  7 purchase totals = $697.65       $759.7442   $759.75   $759.70   $759.80