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 $110.94   6.211%   $117.8305   $117.83   $117.85   $117.80  
  Purchase #2 $161.87   10.108%   $178.2318   $178.23   $178.25   $178.20  
  Purchase #3 $205.75   6.499%   $219.1217   $219.12   $219.10   $219.10  
  Purchase #4 $168.26   9.581%   $184.381   $184.38   $184.40   $184.40  
  Purchase #5 $98.80   7.575%   $106.2841   $106.28   $106.30   $106.30  
  Purchase #6 $177.62   11.417%   $197.8989   $197.90   $197.90   $197.90  
  Purchase #7 $213.77   12.497%   $240.4848   $240.48   $240.50   $240.50  
  7 purchase totals = $1,137.01       $1,244.2328   $1,244.22   $1,244.30   $1,244.20