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 $114.98   8.145%   $124.3451   $124.35   $124.35   $124.30  
  Purchase #2 $183.41   11.777%   $205.0102   $205.01   $205.00   $205.00  
  Purchase #3 $142.29   13.385%   $161.3355   $161.34   $161.35   $161.30  
  Purchase #4 $125.74   11.534%   $140.2429   $140.24   $140.25   $140.20  
  Purchase #5 $37.56   11.144%   $41.7457   $41.75   $41.75   $41.70  
  Purchase #6 $85.55   9.337%   $93.5378   $93.54   $93.55   $93.50  
  Purchase #7 $53.29   5.605%   $56.2769   $56.28   $56.30   $56.30  
  7 purchase totals = $742.82       $822.4941   $822.51   $822.55   $822.30