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 $71.69   6.451%   $76.3147   $76.31   $76.30   $76.30  
  Purchase #2 $205.45   5.782%   $217.3291   $217.33   $217.35   $217.30  
  Purchase #3 $227.44   3.172%   $234.6544   $234.65   $234.65   $234.70  
  Purchase #4 $170.29   12.840%   $192.1552   $192.16   $192.15   $192.20  
  Purchase #5 $199.82   10.781%   $221.3626   $221.36   $221.35   $221.40  
  Purchase #6 $33.49   7.314%   $35.9395   $35.94   $35.95   $35.90  
  Purchase #7 $13.83   12.364%   $15.5399   $15.54   $15.55   $15.50  
  7 purchase totals = $922.01       $993.2954   $993.29   $993.30   $993.30