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 $85.67   9.853%   $94.1111   $94.11   $94.10   $94.10  
  Purchase #2 $160.36   10.309%   $176.8915   $176.89   $176.90   $176.90  
  Purchase #3 $148.68   9.342%   $162.5697   $162.57   $162.55   $162.60  
  Purchase #4 $187.27   10.394%   $206.7348   $206.73   $206.75   $206.70  
  Purchase #5 $15.39   10.403%   $16.991   $16.99   $17.00   $17.00  
  Purchase #6 $8.60   13.590%   $9.7687   $9.77   $9.75   $9.80  
  Purchase #7 $53.43   8.428%   $57.9331   $57.93   $57.95   $57.90  
  7 purchase totals = $659.40       $724.9999   $724.99   $725.00   $725.00