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 $244.56   4.783%   $256.2573   $256.26   $256.25   $256.30  
  Purchase #2 $164.41   12.479%   $184.9267   $184.93   $184.95   $184.90  
  Purchase #3 $202.88   3.710%   $210.4068   $210.41   $210.40   $210.40  
  Purchase #4 $241.65   7.518%   $259.8172   $259.82   $259.80   $259.80  
  Purchase #5 $213.84   11.482%   $238.3931   $238.39   $238.40   $238.40  
  Purchase #6 $211.28   12.369%   $237.4132   $237.41   $237.40   $237.40  
  Purchase #7 $174.34   3.400%   $180.2676   $180.27   $180.25   $180.30  
  7 purchase totals = $1,452.96       $1,567.4819   $1,567.49   $1,567.45   $1,567.50