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 $58.33   11.848%   $65.2409   $65.24   $65.25   $65.20  
  Purchase #2 $206.77   13.519%   $234.7232   $234.72   $234.70   $234.70  
  Purchase #3 $241.48   3.171%   $249.1373   $249.14   $249.15   $249.10  
  Purchase #4 $211.77   6.163%   $224.8214   $224.82   $224.80   $224.80  
  Purchase #5 $47.80   4.486%   $49.9443   $49.94   $49.95   $49.90  
  Purchase #6 $18.38   10.185%   $20.252   $20.25   $20.25   $20.30  
  Purchase #7 $159.67   7.163%   $171.1072   $171.11   $171.10   $171.10  
  7 purchase totals = $944.20       $1,015.2263   $1,015.22   $1,015.20   $1,015.10