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 $10.68   11.821%   $11.9425   $11.94   $11.95   $11.90  
  Purchase #2 $156.61   8.255%   $169.5382   $169.54   $169.55   $169.50  
  Purchase #3 $92.84   5.805%   $98.2294   $98.23   $98.25   $98.20  
  Purchase #4 $226.66   10.727%   $250.9738   $250.97   $250.95   $251.00  
  Purchase #5 $226.69   7.194%   $242.9981   $243.00   $243.00   $243.00  
  Purchase #6 $22.47   9.801%   $24.6723   $24.67   $24.65   $24.70  
  Purchase #7 $183.53   11.712%   $205.025   $205.03   $205.05   $205.00  
  7 purchase totals = $919.48       $1,003.3793   $1,003.38   $1,003.40   $1,003.30