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 $66.91   10.124%   $73.684   $73.68   $73.70   $73.70  
  Purchase #2 $107.57   12.853%   $121.396   $121.40   $121.40   $121.40  
  Purchase #3 $14.31   13.801%   $16.2849   $16.28   $16.30   $16.30  
  Purchase #4 $236.99   5.230%   $249.3846   $249.38   $249.40   $249.40  
  Purchase #5 $176.62   10.832%   $195.7515   $195.75   $195.75   $195.80  
  Purchase #6 $55.38   11.404%   $61.6955   $61.70   $61.70   $61.70  
  Purchase #7 $26.89   5.864%   $28.4668   $28.47   $28.45   $28.50  
  7 purchase totals = $684.67       $746.6633   $746.66   $746.70   $746.80