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 $164.47   10.831%   $182.2837   $182.28   $182.30   $182.30  
  Purchase #2 $27.87   6.381%   $29.6484   $29.65   $29.65   $29.60  
  Purchase #3 $79.85   8.266%   $86.4504   $86.45   $86.45   $86.50  
  Purchase #4 $244.97   6.108%   $259.9328   $259.93   $259.95   $259.90  
  Purchase #5 $78.54   7.234%   $84.2216   $84.22   $84.20   $84.20  
  Purchase #6 $42.43   5.450%   $44.7424   $44.74   $44.75   $44.70  
  Purchase #7 $239.88   10.797%   $265.7798   $265.78   $265.80   $265.80  
  7 purchase totals = $878.01       $953.0591   $953.05   $953.10   $953.00