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 $232.98   11.215%   $259.1087   $259.11   $259.10   $259.10  
  Purchase #2 $87.51   10.791%   $96.9532   $96.95   $96.95   $97.00  
  Purchase #3 $182.71   5.433%   $192.6366   $192.64   $192.65   $192.60  
  Purchase #4 $24.50   11.488%   $27.3146   $27.31   $27.30   $27.30  
  Purchase #5 $168.32   10.130%   $185.3708   $185.37   $185.35   $185.40  
  Purchase #6 $86.26   10.703%   $95.4924   $95.49   $95.50   $95.50  
  Purchase #7 $118.25   8.610%   $128.4313   $128.43   $128.45   $128.40  
  7 purchase totals = $900.53       $985.3076   $985.30   $985.30   $985.30