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 $40.73   3.236%   $42.048   $42.05   $42.05   $42.00  
  Purchase #2 $222.94   8.378%   $241.6179   $241.62   $241.60   $241.60  
  Purchase #3 $47.54   3.208%   $49.0651   $49.07   $49.05   $49.10  
  Purchase #4 $196.28   7.292%   $210.5927   $210.59   $210.60   $210.60  
  Purchase #5 $147.61   11.230%   $164.1866   $164.19   $164.20   $164.20  
  Purchase #6 $96.79   13.818%   $110.1644   $110.16   $110.15   $110.20  
  Purchase #7 $244.41   6.176%   $259.5048   $259.50   $259.50   $259.50  
  7 purchase totals = $996.30       $1,077.1795   $1,077.18   $1,077.15   $1,077.20