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 $44.42   7.246%   $47.6387   $47.64   $47.65   $47.60  
  Purchase #2 $112.70   6.406%   $119.9196   $119.92   $119.90   $119.90  
  Purchase #3 $26.45   12.755%   $29.8237   $29.82   $29.80   $29.80  
  Purchase #4 $199.58   6.468%   $212.4888   $212.49   $212.50   $212.50  
  Purchase #5 $14.82   4.760%   $15.5254   $15.53   $15.55   $15.50  
  Purchase #6 $145.72   13.401%   $165.2479   $165.25   $165.25   $165.20  
  Purchase #7 $195.40   5.490%   $206.1275   $206.13   $206.15   $206.10  
  7 purchase totals = $739.09       $796.7716   $796.78   $796.80   $796.60