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 $67.76   8.390%   $73.4451   $73.45   $73.45   $73.40  
  Purchase #2 $196.99   10.594%   $217.8591   $217.86   $217.85   $217.90  
  Purchase #3 $152.49   9.223%   $166.5542   $166.55   $166.55   $166.60  
  Purchase #4 $32.61   8.694%   $35.4451   $35.45   $35.45   $35.40  
  Purchase #5 $62.50   6.806%   $66.7538   $66.75   $66.75   $66.80  
  Purchase #6 $70.53   3.497%   $72.9964   $73.00   $73.00   $73.00  
  Purchase #7 $171.82   10.394%   $189.679   $189.68   $189.70   $189.70  
  7 purchase totals = $754.70       $822.7327   $822.74   $822.75   $822.80