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 $58.78   9.367%   $64.2859   $64.29   $64.30   $64.30  
  Purchase #2 $129.60   13.656%   $147.2982   $147.30   $147.30   $147.30  
  Purchase #3 $95.42   3.733%   $98.982   $98.98   $99.00   $99.00  
  Purchase #4 $94.30   7.194%   $101.0839   $101.08   $101.10   $101.10  
  Purchase #5 $164.63   11.106%   $182.9138   $182.91   $182.90   $182.90  
  Purchase #6 $214.98   8.803%   $233.9047   $233.90   $233.90   $233.90  
  Purchase #7 $185.61   10.353%   $204.8262   $204.83   $204.85   $204.80  
  7 purchase totals = $943.32       $1,033.2947   $1,033.29   $1,033.35   $1,033.30