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 $137.34   11.765%   $153.4981   $153.50   $153.50   $153.50  
  Purchase #2 $159.76   10.686%   $176.832   $176.83   $176.85   $176.80  
  Purchase #3 $214.34   8.846%   $233.3005   $233.30   $233.30   $233.30  
  Purchase #4 $81.68   5.569%   $86.2288   $86.23   $86.25   $86.20  
  Purchase #5 $122.75   3.335%   $126.8437   $126.84   $126.85   $126.80  
  Purchase #6 $52.37   5.816%   $55.4158   $55.42   $55.40   $55.40  
  Purchase #7 $86.29   9.353%   $94.3607   $94.36   $94.35   $94.40  
  7 purchase totals = $854.53       $926.4796   $926.48   $926.50   $926.40