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 $74.82   12.524%   $84.1905   $84.19   $84.20   $84.20  
  Purchase #2 $236.78   10.457%   $261.5401   $261.54   $261.55   $261.50  
  Purchase #3 $99.63   5.641%   $105.2501   $105.25   $105.25   $105.30  
  Purchase #4 $210.53   4.464%   $219.9281   $219.93   $219.95   $219.90  
  Purchase #5 $18.53   9.692%   $20.3259   $20.33   $20.35   $20.30  
  Purchase #6 $192.87   4.399%   $201.3544   $201.35   $201.35   $201.40  
  Purchase #7 $53.53   10.295%   $59.0409   $59.04   $59.05   $59.00  
  7 purchase totals = $886.69       $951.6300   $951.63   $951.70   $951.60