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 $239.78   11.121%   $266.4459   $266.45   $266.45   $266.40  
  Purchase #2 $119.47   4.434%   $124.7673   $124.77   $124.75   $124.80  
  Purchase #3 $238.27   9.130%   $260.0241   $260.02   $260.00   $260.00  
  Purchase #4 $115.79   9.552%   $126.8503   $126.85   $126.85   $126.90  
  Purchase #5 $44.84   4.463%   $46.8412   $46.84   $46.85   $46.80  
  Purchase #6 $19.38   11.698%   $21.6471   $21.65   $21.65   $21.60  
  Purchase #7 $204.61   9.836%   $224.7354   $224.74   $224.75   $224.70  
  7 purchase totals = $982.14       $1,071.3113   $1,071.32   $1,071.30   $1,071.20