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 $182.62   6.477%   $194.4483   $194.45   $194.45   $194.40  
  Purchase #2 $85.99   8.557%   $93.3482   $93.35   $93.35   $93.30  
  Purchase #3 $178.60   12.262%   $200.4999   $200.50   $200.50   $200.50  
  Purchase #4 $236.58   5.391%   $249.334   $249.33   $249.35   $249.30  
  Purchase #5 $77.31   13.766%   $87.9525   $87.95   $87.95   $88.00  
  Purchase #6 $41.85   8.246%   $45.301   $45.30   $45.30   $45.30  
  Purchase #7 $76.65   12.706%   $86.3891   $86.39   $86.40   $86.40  
  7 purchase totals = $879.60       $957.2730   $957.27   $957.30   $957.20