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 $241.96   10.867%   $268.2538   $268.25   $268.25   $268.30  
  Purchase #2 $63.93   11.652%   $71.3791   $71.38   $71.40   $71.40  
  Purchase #3 $193.33   13.113%   $218.6814   $218.68   $218.70   $218.70  
  Purchase #4 $224.35   11.316%   $249.7374   $249.74   $249.75   $249.70  
  Purchase #5 $218.52   6.684%   $233.1259   $233.13   $233.15   $233.10  
  Purchase #6 $126.98   4.817%   $133.0966   $133.10   $133.10   $133.10  
  Purchase #7 $96.83   7.538%   $104.129   $104.13   $104.15   $104.10  
  7 purchase totals = $1,165.90       $1,278.4032   $1,278.41   $1,278.50   $1,278.40