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 $129.25   10.839%   $143.2594   $143.26   $143.25   $143.30  
  Purchase #2 $133.41   11.199%   $148.3506   $148.35   $148.35   $148.40  
  Purchase #3 $169.78   4.719%   $177.7919   $177.79   $177.80   $177.80  
  Purchase #4 $57.73   9.495%   $63.2115   $63.21   $63.20   $63.20  
  Purchase #5 $184.45   6.534%   $196.502   $196.50   $196.50   $196.50  
  Purchase #6 $124.49   9.358%   $136.1398   $136.14   $136.15   $136.10  
  Purchase #7 $139.76   13.263%   $158.2964   $158.30   $158.30   $158.30  
  7 purchase totals = $938.87       $1,023.5516   $1,023.55   $1,023.55   $1,023.60