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 $57.66   8.108%   $62.3351   $62.34   $62.35   $62.30  
  Purchase #2 $82.31   13.321%   $93.2745   $93.27   $93.25   $93.30  
  Purchase #3 $139.62   5.789%   $147.7026   $147.70   $147.70   $147.70  
  Purchase #4 $234.42   4.588%   $245.1752   $245.18   $245.20   $245.20  
  Purchase #5 $36.38   13.271%   $41.208   $41.21   $41.20   $41.20  
  Purchase #6 $49.39   8.611%   $53.643   $53.64   $53.65   $53.60  
  Purchase #7 $47.55   7.763%   $51.2413   $51.24   $51.25   $51.20  
  7 purchase totals = $647.33       $694.5797   $694.58   $694.60   $694.50