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 $110.53   13.607%   $125.5698   $125.57   $125.55   $125.60  
  Purchase #2 $201.45   6.504%   $214.5523   $214.55   $214.55   $214.60  
  Purchase #3 $8.60   13.476%   $9.7589   $9.76   $9.75   $9.80  
  Purchase #4 $163.48   5.680%   $172.7657   $172.77   $172.75   $172.80  
  Purchase #5 $124.86   11.503%   $139.2226   $139.22   $139.20   $139.20  
  Purchase #6 $173.39   6.122%   $184.0049   $184.00   $184.00   $184.00  
  Purchase #7 $93.97   5.316%   $98.9654   $98.97   $98.95   $99.00  
  7 purchase totals = $876.28       $944.8396   $944.84   $944.75   $945.00