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 $64.46   13.409%   $73.1034   $73.10   $73.10   $73.10  
  Purchase #2 $193.99   10.486%   $214.3318   $214.33   $214.35   $214.30  
  Purchase #3 $241.54   5.476%   $254.7667   $254.77   $254.75   $254.80  
  Purchase #4 $101.62   9.297%   $111.0676   $111.07   $111.05   $111.10  
  Purchase #5 $152.85   6.633%   $162.9885   $162.99   $163.00   $163.00  
  Purchase #6 $249.98   10.347%   $275.8454   $275.85   $275.85   $275.80  
  Purchase #7 $137.53   10.242%   $151.6158   $151.62   $151.60   $151.60  
  7 purchase totals = $1,141.97       $1,243.7192   $1,243.73   $1,243.70   $1,243.70