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 $240.39   8.178%   $260.0491   $260.05   $260.05   $260.00  
  Purchase #2 $91.36   5.497%   $96.3821   $96.38   $96.40   $96.40  
  Purchase #3 $49.34   5.355%   $51.9822   $51.98   $52.00   $52.00  
  Purchase #4 $68.25   7.390%   $73.2937   $73.29   $73.30   $73.30  
  Purchase #5 $179.25   9.277%   $195.879   $195.88   $195.90   $195.90  
  Purchase #6 $46.75   9.826%   $51.3437   $51.34   $51.35   $51.30  
  Purchase #7 $48.94   9.698%   $53.6862   $53.69   $53.70   $53.70  
  7 purchase totals = $724.28       $782.6160   $782.61   $782.70   $782.60