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 $73.75   12.116%   $82.6856   $82.69   $82.70   $82.70  
  Purchase #2 $202.50   5.156%   $212.9409   $212.94   $212.95   $212.90  
  Purchase #3 $164.56   3.174%   $169.7831   $169.78   $169.80   $169.80  
  Purchase #4 $101.79   13.873%   $115.9113   $115.91   $115.90   $115.90  
  Purchase #5 $91.33   12.808%   $103.0275   $103.03   $103.05   $103.00  
  Purchase #6 $111.73   9.747%   $122.6203   $122.62   $122.60   $122.60  
  Purchase #7 $183.48   12.539%   $206.4866   $206.49   $206.50   $206.50  
  7 purchase totals = $929.14       $1,013.4553   $1,013.46   $1,013.50   $1,013.40