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 $46.79   8.546%   $50.7887   $50.79   $50.80   $50.80  
  Purchase #2 $183.54   7.105%   $196.5805   $196.58   $196.60   $196.60  
  Purchase #3 $69.30   7.848%   $74.7387   $74.74   $74.75   $74.70  
  Purchase #4 $96.34   13.145%   $109.0039   $109.00   $109.00   $109.00  
  Purchase #5 $233.99   13.490%   $265.5553   $265.56   $265.55   $265.60  
  Purchase #6 $69.80   7.683%   $75.1627   $75.16   $75.15   $75.20  
  Purchase #7 $193.53   10.521%   $213.8913   $213.89   $213.90   $213.90  
  7 purchase totals = $893.29       $985.7211   $985.72   $985.75   $985.80