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 $101.82   8.748%   $110.7272   $110.73   $110.75   $110.70  
  Purchase #2 $220.99   10.688%   $244.6094   $244.61   $244.60   $244.60  
  Purchase #3 $103.98   13.659%   $118.1826   $118.18   $118.20   $118.20  
  Purchase #4 $58.71   8.687%   $63.8101   $63.81   $63.80   $63.80  
  Purchase #5 $130.64   9.356%   $142.8627   $142.86   $142.85   $142.90  
  Purchase #6 $81.87   12.290%   $91.9318   $91.93   $91.95   $91.90  
  Purchase #7 $233.41   8.260%   $252.6897   $252.69   $252.70   $252.70  
  7 purchase totals = $931.42       $1,024.8135   $1,024.81   $1,024.85   $1,024.80