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 $59.34   7.262%   $63.6493   $63.65   $63.65   $63.60  
  Purchase #2 $18.69   12.830%   $21.0879   $21.09   $21.10   $21.10  
  Purchase #3 $174.84   11.539%   $195.0148   $195.01   $195.00   $195.00  
  Purchase #4 $181.48   11.271%   $201.9346   $201.93   $201.95   $201.90  
  Purchase #5 $105.60   10.428%   $116.612   $116.61   $116.60   $116.60  
  Purchase #6 $47.84   8.681%   $51.993   $51.99   $52.00   $52.00  
  Purchase #7 $150.36   7.479%   $161.6054   $161.61   $161.60   $161.60  
  7 purchase totals = $738.15       $811.8970   $811.89   $811.90   $811.80