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 $235.95   3.437%   $244.0596   $244.06   $244.05   $244.10  
  Purchase #2 $129.59   12.406%   $145.6669   $145.67   $145.65   $145.70  
  Purchase #3 $97.88   13.457%   $111.0517   $111.05   $111.05   $111.10  
  Purchase #4 $238.98   3.852%   $248.1855   $248.19   $248.20   $248.20  
  Purchase #5 $12.67   4.673%   $13.2621   $13.26   $13.25   $13.30  
  Purchase #6 $114.68   9.219%   $125.2523   $125.25   $125.25   $125.30  
  Purchase #7 $167.38   11.128%   $186.006   $186.01   $186.00   $186.00  
  7 purchase totals = $997.13       $1,073.4841   $1,073.49   $1,073.45   $1,073.70