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 $34.87   3.706%   $36.1623   $36.16   $36.15   $36.20  
  Purchase #2 $53.39   12.278%   $59.9452   $59.95   $59.95   $59.90  
  Purchase #3 $168.87   10.366%   $186.3751   $186.38   $186.40   $186.40  
  Purchase #4 $168.44   11.814%   $188.3395   $188.34   $188.35   $188.30  
  Purchase #5 $89.49   7.674%   $96.3575   $96.36   $96.35   $96.40  
  Purchase #6 $16.96   3.144%   $17.4932   $17.49   $17.50   $17.50  
  Purchase #7 $240.33   10.634%   $265.8867   $265.89   $265.90   $265.90  
  7 purchase totals = $772.35       $850.5595   $850.57   $850.60   $850.60