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 $240.56   3.643%   $249.3236   $249.32   $249.30   $249.30  
  Purchase #2 $56.33   3.602%   $58.359   $58.36   $58.35   $58.40  
  Purchase #3 $116.74   6.177%   $123.951   $123.95   $123.95   $124.00  
  Purchase #4 $91.97   4.826%   $96.4085   $96.41   $96.40   $96.40  
  Purchase #5 $90.47   11.723%   $101.0758   $101.08   $101.10   $101.10  
  Purchase #6 $216.48   3.427%   $223.8988   $223.90   $223.90   $223.90  
  Purchase #7 $76.63   3.587%   $79.3787   $79.38   $79.40   $79.40  
  7 purchase totals = $889.18       $932.3954   $932.40   $932.40   $932.50