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 $68.33   8.408%   $74.0752   $74.08   $74.10   $74.10  
  Purchase #2 $23.34   11.534%   $26.032   $26.03   $26.05   $26.00  
  Purchase #3 $48.35   6.134%   $51.3158   $51.32   $51.30   $51.30  
  Purchase #4 $34.49   7.132%   $36.9498   $36.95   $36.95   $36.90  
  Purchase #5 $118.81   7.342%   $127.533   $127.53   $127.55   $127.50  
  Purchase #6 $175.90   12.559%   $197.9913   $197.99   $198.00   $198.00  
  Purchase #7 $153.87   5.308%   $162.0374   $162.04   $162.05   $162.00  
  7 purchase totals = $623.09       $675.9345   $675.94   $676.00   $675.80