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 $103.61   10.297%   $114.2787   $114.28   $114.30   $114.30  
  Purchase #2 $179.58   12.704%   $202.3938   $202.39   $202.40   $202.40  
  Purchase #3 $142.98   12.731%   $161.1828   $161.18   $161.20   $161.20  
  Purchase #4 $68.66   4.215%   $71.554   $71.55   $71.55   $71.60  
  Purchase #5 $127.54   12.661%   $143.6878   $143.69   $143.70   $143.70  
  Purchase #6 $48.44   5.737%   $51.219   $51.22   $51.20   $51.20  
  Purchase #7 $67.94   9.788%   $74.59   $74.59   $74.60   $74.60  
  7 purchase totals = $738.75       $818.9061   $818.90   $818.95   $819.00