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 $34.26   12.467%   $38.5312   $38.53   $38.55   $38.50  
  Purchase #2 $167.32   4.863%   $175.4568   $175.46   $175.45   $175.50  
  Purchase #3 $88.41   7.632%   $95.1575   $95.16   $95.15   $95.20  
  Purchase #4 $101.55   5.412%   $107.0459   $107.05   $107.05   $107.00  
  Purchase #5 $213.69   9.163%   $233.2704   $233.27   $233.25   $233.30  
  Purchase #6 $204.98   11.811%   $229.1902   $229.19   $229.20   $229.20  
  Purchase #7 $64.41   5.418%   $67.8997   $67.90   $67.90   $67.90  
  7 purchase totals = $874.62       $946.5517   $946.56   $946.55   $946.60