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 $84.82   8.551%   $92.073   $92.07   $92.05   $92.10  
  Purchase #2 $158.98   5.813%   $168.2215   $168.22   $168.20   $168.20  
  Purchase #3 $177.99   10.263%   $196.2571   $196.26   $196.25   $196.30  
  Purchase #4 $69.98   10.564%   $77.3727   $77.37   $77.35   $77.40  
  Purchase #5 $60.51   7.273%   $64.9109   $64.91   $64.90   $64.90  
  Purchase #6 $20.40   9.549%   $22.348   $22.35   $22.35   $22.30  
  Purchase #7 $177.26   7.733%   $190.9675   $190.97   $190.95   $191.00  
  7 purchase totals = $749.94       $812.1507   $812.15   $812.05   $812.20