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 $54.39   5.504%   $57.3836   $57.38   $57.40   $57.40  
  Purchase #2 $171.67   6.316%   $182.5127   $182.51   $182.50   $182.50  
  Purchase #3 $144.44   13.582%   $164.0578   $164.06   $164.05   $164.10  
  Purchase #4 $241.56   5.792%   $255.5512   $255.55   $255.55   $255.60  
  Purchase #5 $83.44   5.545%   $88.0667   $88.07   $88.05   $88.10  
  Purchase #6 $124.41   4.411%   $129.8977   $129.90   $129.90   $129.90  
  Purchase #7 $118.25   5.800%   $125.1085   $125.11   $125.10   $125.10  
  7 purchase totals = $938.16       $1,002.5782   $1,002.58   $1,002.55   $1,002.70