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 $68.74   13.412%   $77.9594   $77.96   $77.95   $78.00  
  Purchase #2 $119.66   4.622%   $125.1907   $125.19   $125.20   $125.20  
  Purchase #3 $59.70   10.819%   $66.1589   $66.16   $66.15   $66.20  
  Purchase #4 $81.88   7.586%   $88.0914   $88.09   $88.10   $88.10  
  Purchase #5 $153.99   12.250%   $172.8538   $172.85   $172.85   $172.90  
  Purchase #6 $161.70   4.225%   $168.5318   $168.53   $168.55   $168.50  
  Purchase #7 $135.63   5.328%   $142.8564   $142.86   $142.85   $142.90  
  7 purchase totals = $781.30       $841.6424   $841.64   $841.65   $841.80