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 $63.74   7.732%   $68.6684   $68.67   $68.65   $68.70  
  Purchase #2 $88.28   4.674%   $92.4062   $92.41   $92.40   $92.40  
  Purchase #3 $136.40   3.271%   $140.8616   $140.86   $140.85   $140.90  
  Purchase #4 $86.87   8.103%   $93.9091   $93.91   $93.90   $93.90  
  Purchase #5 $54.82   9.526%   $60.0422   $60.04   $60.05   $60.00  
  Purchase #6 $219.95   13.501%   $249.6454   $249.65   $249.65   $249.60  
  Purchase #7 $84.47   6.540%   $89.9943   $89.99   $90.00   $90.00  
  7 purchase totals = $734.53       $795.5272   $795.53   $795.50   $795.50