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 $83.40   11.104%   $92.6607   $92.66   $92.65   $92.70  
  Purchase #2 $24.41   11.407%   $27.1944   $27.19   $27.20   $27.20  
  Purchase #3 $226.43   12.741%   $255.2794   $255.28   $255.30   $255.30  
  Purchase #4 $111.73   13.650%   $126.9811   $126.98   $127.00   $127.00  
  Purchase #5 $48.90   5.560%   $51.6188   $51.62   $51.60   $51.60  
  Purchase #6 $227.74   8.410%   $246.8929   $246.89   $246.90   $246.90  
  Purchase #7 $112.71   4.714%   $118.0231   $118.02   $118.00   $118.00  
  7 purchase totals = $835.32       $918.6504   $918.64   $918.65   $918.70