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 $216.32   13.504%   $245.5319   $245.53   $245.55   $245.50  
  Purchase #2 $92.75   11.283%   $103.215   $103.22   $103.20   $103.20  
  Purchase #3 $183.42   7.764%   $197.6607   $197.66   $197.65   $197.70  
  Purchase #4 $26.70   8.442%   $28.954   $28.95   $28.95   $29.00  
  Purchase #5 $46.81   6.697%   $49.9449   $49.94   $49.95   $49.90  
  Purchase #6 $22.39   6.565%   $23.8599   $23.86   $23.85   $23.90  
  Purchase #7 $111.28   6.290%   $118.2795   $118.28   $118.30   $118.30  
  7 purchase totals = $699.67       $767.4459   $767.44   $767.45   $767.50