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 $242.39   11.196%   $269.528   $269.53   $269.55   $269.50  
  Purchase #2 $15.91   13.297%   $18.0256   $18.03   $18.05   $18.00  
  Purchase #3 $56.90   9.266%   $62.1724   $62.17   $62.15   $62.20  
  Purchase #4 $54.66   4.846%   $57.3088   $57.31   $57.30   $57.30  
  Purchase #5 $106.62   10.249%   $117.5475   $117.55   $117.55   $117.50  
  Purchase #6 $234.89   6.382%   $249.8807   $249.88   $249.90   $249.90  
  Purchase #7 $177.94   3.489%   $184.1483   $184.15   $184.15   $184.10  
  7 purchase totals = $889.31       $958.6113   $958.62   $958.65   $958.50