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 $56.74   13.864%   $64.6064   $64.61   $64.60   $64.60  
  Purchase #2 $125.69   4.454%   $131.2882   $131.29   $131.30   $131.30  
  Purchase #3 $44.86   7.493%   $48.2214   $48.22   $48.20   $48.20  
  Purchase #4 $206.50   6.672%   $220.2777   $220.28   $220.30   $220.30  
  Purchase #5 $124.90   4.712%   $130.7853   $130.79   $130.80   $130.80  
  Purchase #6 $174.38   6.838%   $186.3041   $186.30   $186.30   $186.30  
  Purchase #7 $240.73   3.754%   $249.767   $249.77   $249.75   $249.80  
  7 purchase totals = $973.80       $1,031.2501   $1,031.26   $1,031.25   $1,031.30