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 $182.68   13.737%   $207.7748   $207.77   $207.75   $207.80  
  Purchase #2 $34.60   12.838%   $39.0419   $39.04   $39.05   $39.00  
  Purchase #3 $5.94   5.341%   $6.2573   $6.26   $6.25   $6.30  
  Purchase #4 $235.62   11.315%   $262.2804   $262.28   $262.30   $262.30  
  Purchase #5 $111.43   13.114%   $126.0429   $126.04   $126.05   $126.00  
  Purchase #6 $217.63   4.104%   $226.5615   $226.56   $226.55   $226.60  
  Purchase #7 $233.28   7.159%   $249.9805   $249.98   $250.00   $250.00  
  7 purchase totals = $1,021.18       $1,117.9393   $1,117.93   $1,117.95   $1,118.00