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 $117.94   7.458%   $126.736   $126.74   $126.75   $126.70  
  Purchase #2 $27.94   6.754%   $29.8271   $29.83   $29.85   $29.80  
  Purchase #3 $69.31   12.466%   $77.9502   $77.95   $77.95   $78.00  
  Purchase #4 $213.45   5.275%   $224.7095   $224.71   $224.70   $224.70  
  Purchase #5 $185.47   10.632%   $205.1892   $205.19   $205.20   $205.20  
  Purchase #6 $130.75   13.359%   $148.2169   $148.22   $148.20   $148.20  
  Purchase #7 $155.62   13.665%   $176.8855   $176.89   $176.90   $176.90  
  7 purchase totals = $900.48       $989.5144   $989.53   $989.55   $989.50