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 $211.29   6.359%   $224.7259   $224.73   $224.75   $224.70  
  Purchase #2 $95.40   3.603%   $98.8373   $98.84   $98.85   $98.80  
  Purchase #3 $11.67   10.389%   $12.8824   $12.88   $12.90   $12.90  
  Purchase #4 $59.99   8.181%   $64.8978   $64.90   $64.90   $64.90  
  Purchase #5 $224.32   6.810%   $239.5962   $239.60   $239.60   $239.60  
  Purchase #6 $42.27   10.502%   $46.7092   $46.71   $46.70   $46.70  
  Purchase #7 $120.68   13.121%   $136.5144   $136.51   $136.50   $136.50  
  7 purchase totals = $765.62       $824.1632   $824.17   $824.20   $824.10