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 $205.36   6.387%   $218.4763   $218.48   $218.50   $218.50  
  Purchase #2 $101.46   12.240%   $113.8787   $113.88   $113.90   $113.90  
  Purchase #3 $21.71   4.199%   $22.6216   $22.62   $22.60   $22.60  
  Purchase #4 $195.46   11.307%   $217.5607   $217.56   $217.55   $217.60  
  Purchase #5 $221.51   4.488%   $231.4514   $231.45   $231.45   $231.50  
  Purchase #6 $22.49   4.825%   $23.5751   $23.58   $23.60   $23.60  
  Purchase #7 $118.58   6.598%   $126.4039   $126.40   $126.40   $126.40  
  7 purchase totals = $886.57       $953.9677   $953.97   $954.00   $954.10