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 $14.95   13.118%   $16.9111   $16.91   $16.90   $16.90  
  Purchase #2 $192.73   4.300%   $201.0174   $201.02   $201.00   $201.00  
  Purchase #3 $47.47   4.465%   $49.5895   $49.59   $49.60   $49.60  
  Purchase #4 $176.92   7.485%   $190.1625   $190.16   $190.15   $190.20  
  Purchase #5 $55.47   6.423%   $59.0328   $59.03   $59.05   $59.00  
  Purchase #6 $45.40   12.182%   $50.9306   $50.93   $50.95   $50.90  
  Purchase #7 $162.75   9.791%   $178.6849   $178.68   $178.70   $178.70  
  7 purchase totals = $695.69       $746.3288   $746.32   $746.35   $746.30