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 $48.38   12.242%   $54.3027   $54.30   $54.30   $54.30  
  Purchase #2 $210.97   5.712%   $223.0206   $223.02   $223.00   $223.00  
  Purchase #3 $178.73   7.847%   $192.7549   $192.75   $192.75   $192.80  
  Purchase #4 $71.37   5.364%   $75.1983   $75.20   $75.20   $75.20  
  Purchase #5 $170.56   13.676%   $193.8858   $193.89   $193.90   $193.90  
  Purchase #6 $109.46   4.243%   $114.1044   $114.10   $114.10   $114.10  
  Purchase #7 $92.53   5.284%   $97.4193   $97.42   $97.40   $97.40  
  7 purchase totals = $882.00       $950.6860   $950.68   $950.65   $950.70