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 $234.99   9.169%   $256.5362   $256.54   $256.55   $256.50  
  Purchase #2 $20.82   8.585%   $22.6074   $22.61   $22.60   $22.60  
  Purchase #3 $43.60   8.629%   $47.3622   $47.36   $47.35   $47.40  
  Purchase #4 $250.90   7.814%   $270.5053   $270.51   $270.50   $270.50  
  Purchase #5 $72.69   9.696%   $79.738   $79.74   $79.75   $79.70  
  Purchase #6 $129.71   5.854%   $137.3032   $137.30   $137.30   $137.30  
  Purchase #7 $241.78   7.399%   $259.6693   $259.67   $259.65   $259.70  
  7 purchase totals = $994.49       $1,073.7216   $1,073.73   $1,073.70   $1,073.70