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 $52.87   7.355%   $56.7586   $56.76   $56.75   $56.80  
  Purchase #2 $125.90   5.766%   $133.1594   $133.16   $133.15   $133.20  
  Purchase #3 $234.60   4.415%   $244.9576   $244.96   $244.95   $245.00  
  Purchase #4 $81.79   6.785%   $87.3395   $87.34   $87.35   $87.30  
  Purchase #5 $9.84   3.549%   $10.1892   $10.19   $10.20   $10.20  
  Purchase #6 $171.62   8.374%   $185.9915   $185.99   $186.00   $186.00  
  Purchase #7 $62.31   6.816%   $66.557   $66.56   $66.55   $66.60  
  7 purchase totals = $738.93       $784.9528   $784.96   $784.95   $785.10