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 $48.36   13.654%   $54.9631   $54.96   $54.95   $55.00  
  Purchase #2 $103.70   9.308%   $113.3524   $113.35   $113.35   $113.40  
  Purchase #3 $225.69   8.381%   $244.6051   $244.61   $244.60   $244.60  
  Purchase #4 $153.54   9.727%   $168.4748   $168.47   $168.45   $168.50  
  Purchase #5 $84.73   3.107%   $87.3626   $87.36   $87.35   $87.40  
  Purchase #6 $192.29   7.210%   $206.1541   $206.15   $206.15   $206.20  
  Purchase #7 $74.42   10.517%   $82.2468   $82.25   $82.25   $82.20  
  7 purchase totals = $882.73       $957.1589   $957.15   $957.10   $957.30