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 $60.97   5.538%   $64.3465   $64.35   $64.35   $64.30  
  Purchase #2 $239.54   12.803%   $270.2083   $270.21   $270.20   $270.20  
  Purchase #3 $155.78   13.565%   $176.9116   $176.91   $176.90   $176.90  
  Purchase #4 $211.82   8.765%   $230.386   $230.39   $230.40   $230.40  
  Purchase #5 $143.71   13.139%   $162.5921   $162.59   $162.60   $162.60  
  Purchase #6 $6.62   13.806%   $7.534   $7.53   $7.55   $7.50  
  Purchase #7 $229.70   13.463%   $260.6245   $260.62   $260.60   $260.60  
  7 purchase totals = $1,048.14       $1,172.6030   $1,172.60   $1,172.60   $1,172.50