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 $208.95   7.509%   $224.6401   $224.64   $224.65   $224.60  
  Purchase #2 $6.48   9.609%   $7.1027   $7.10   $7.10   $7.10  
  Purchase #3 $59.40   9.426%   $64.999   $65.00   $65.00   $65.00  
  Purchase #4 $188.36   11.172%   $209.4036   $209.40   $209.40   $209.40  
  Purchase #5 $126.29   4.580%   $132.0741   $132.07   $132.05   $132.10  
  Purchase #6 $9.31   11.854%   $10.4136   $10.41   $10.40   $10.40  
  Purchase #7 $148.42   9.606%   $162.6772   $162.68   $162.70   $162.70  
  7 purchase totals = $747.21       $811.3103   $811.30   $811.30   $811.30