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 $68.36   11.843%   $76.4559   $76.46   $76.45   $76.50  
  Purchase #2 $21.85   9.835%   $23.9989   $24.00   $24.00   $24.00  
  Purchase #3 $248.72   11.151%   $276.4548   $276.45   $276.45   $276.50  
  Purchase #4 $250.83   11.539%   $279.7733   $279.77   $279.75   $279.80  
  Purchase #5 $75.31   12.148%   $84.4587   $84.46   $84.45   $84.50  
  Purchase #6 $8.90   5.607%   $9.399   $9.40   $9.40   $9.40  
  Purchase #7 $238.93   10.819%   $264.7798   $264.78   $264.80   $264.80  
  7 purchase totals = $912.90       $1,015.3204   $1,015.32   $1,015.30   $1,015.50