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 $248.67   4.403%   $259.6189   $259.62   $259.60   $259.60  
  Purchase #2 $177.92   3.830%   $184.7343   $184.73   $184.75   $184.70  
  Purchase #3 $188.45   8.461%   $204.3948   $204.39   $204.40   $204.40  
  Purchase #4 $106.61   13.746%   $121.2646   $121.26   $121.25   $121.30  
  Purchase #5 $190.68   13.547%   $216.5114   $216.51   $216.50   $216.50  
  Purchase #6 $207.27   4.649%   $216.906   $216.91   $216.90   $216.90  
  Purchase #7 $232.29   3.238%   $239.8116   $239.81   $239.80   $239.80  
  7 purchase totals = $1,351.89       $1,443.2416   $1,443.23   $1,443.20   $1,443.20