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 $244.39   8.325%   $264.7355   $264.74   $264.75   $264.70  
  Purchase #2 $46.69   9.427%   $51.0915   $51.09   $51.10   $51.10  
  Purchase #3 $47.32   12.186%   $53.0864   $53.09   $53.10   $53.10  
  Purchase #4 $180.87   8.354%   $195.9799   $195.98   $196.00   $196.00  
  Purchase #5 $67.64   13.575%   $76.8221   $76.82   $76.80   $76.80  
  Purchase #6 $167.78   11.409%   $186.922   $186.92   $186.90   $186.90  
  Purchase #7 $72.95   8.752%   $79.3346   $79.33   $79.35   $79.30  
  7 purchase totals = $827.64       $907.9720   $907.97   $908.00   $907.90