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 $8.59   13.663%   $9.7637   $9.76   $9.75   $9.80  
  Purchase #2 $247.41   7.112%   $265.0058   $265.01   $265.00   $265.00  
  Purchase #3 $61.83   7.317%   $66.3541   $66.35   $66.35   $66.40  
  Purchase #4 $197.29   9.127%   $215.2967   $215.30   $215.30   $215.30  
  Purchase #5 $71.51   9.643%   $78.4057   $78.41   $78.40   $78.40  
  Purchase #6 $172.53   10.807%   $191.1753   $191.18   $191.20   $191.20  
  Purchase #7 $196.53   10.413%   $216.9947   $216.99   $217.00   $217.00  
  7 purchase totals = $955.69       $1,042.9960   $1,043.00   $1,043.00   $1,043.10