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 $54.65   5.660%   $57.7432   $57.74   $57.75   $57.70  
  Purchase #2 $238.99   7.516%   $256.9525   $256.95   $256.95   $257.00  
  Purchase #3 $88.65   8.680%   $96.3448   $96.34   $96.35   $96.30  
  Purchase #4 $249.46   13.754%   $283.7707   $283.77   $283.75   $283.80  
  Purchase #5 $134.83   11.754%   $150.6779   $150.68   $150.70   $150.70  
  Purchase #6 $8.88   6.306%   $9.44   $9.44   $9.45   $9.40  
  Purchase #7 $234.70   11.611%   $261.951   $261.95   $261.95   $262.00  
  7 purchase totals = $1,010.16       $1,116.8801   $1,116.87   $1,116.90   $1,116.90