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 $182.78   12.598%   $205.8066   $205.81   $205.80   $205.80  
  Purchase #2 $92.95   3.790%   $96.4728   $96.47   $96.45   $96.50  
  Purchase #3 $42.35   13.416%   $48.0317   $48.03   $48.05   $48.00  
  Purchase #4 $67.36   9.331%   $73.6454   $73.65   $73.65   $73.60  
  Purchase #5 $192.49   8.728%   $209.2905   $209.29   $209.30   $209.30  
  Purchase #6 $103.26   6.196%   $109.658   $109.66   $109.65   $109.70  
  Purchase #7 $9.87   7.727%   $10.6327   $10.63   $10.65   $10.60  
  7 purchase totals = $691.06       $753.5377   $753.54   $753.55   $753.50