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 $41.60   4.307%   $43.3917   $43.39   $43.40   $43.40  
  Purchase #2 $14.87   10.429%   $16.4208   $16.42   $16.40   $16.40  
  Purchase #3 $102.94   4.828%   $107.9099   $107.91   $107.90   $107.90  
  Purchase #4 $218.31   13.634%   $248.0744   $248.07   $248.05   $248.10  
  Purchase #5 $248.61   10.494%   $274.6991   $274.70   $274.70   $274.70  
  Purchase #6 $130.60   10.414%   $144.2007   $144.20   $144.20   $144.20  
  Purchase #7 $210.98   12.143%   $236.5993   $236.60   $236.60   $236.60  
  7 purchase totals = $967.91       $1,071.2959   $1,071.29   $1,071.25   $1,071.30