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 $243.98   9.230%   $266.4994   $266.50   $266.50   $266.50  
  Purchase #2 $179.40   4.610%   $187.6703   $187.67   $187.65   $187.70  
  Purchase #3 $237.39   3.301%   $245.2262   $245.23   $245.25   $245.20  
  Purchase #4 $69.41   8.512%   $75.3182   $75.32   $75.30   $75.30  
  Purchase #5 $229.80   8.808%   $250.0408   $250.04   $250.05   $250.00  
  Purchase #6 $71.39   4.201%   $74.3891   $74.39   $74.40   $74.40  
  Purchase #7 $248.30   7.780%   $267.6177   $267.62   $267.60   $267.60  
  7 purchase totals = $1,279.67       $1,366.7617   $1,366.77   $1,366.75   $1,366.70