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 $243.93   5.167%   $256.5339   $256.53   $256.55   $256.50  
  Purchase #2 $22.67   13.393%   $25.7062   $25.71   $25.70   $25.70  
  Purchase #3 $227.44   9.590%   $249.2515   $249.25   $249.25   $249.30  
  Purchase #4 $236.49   7.523%   $254.2811   $254.28   $254.30   $254.30  
  Purchase #5 $16.79   13.348%   $19.0311   $19.03   $19.05   $19.00  
  Purchase #6 $148.96   6.824%   $159.125   $159.13   $159.15   $159.10  
  Purchase #7 $46.90   6.534%   $49.9644   $49.96   $49.95   $50.00  
  7 purchase totals = $943.18       $1,013.8932   $1,013.89   $1,013.95   $1,013.90