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 $68.80   7.207%   $73.7584   $73.76   $73.75   $73.80  
  Purchase #2 $205.77   3.211%   $212.3773   $212.38   $212.40   $212.40  
  Purchase #3 $155.35   5.383%   $163.7125   $163.71   $163.70   $163.70  
  Purchase #4 $113.86   4.400%   $118.8698   $118.87   $118.85   $118.90  
  Purchase #5 $195.91   6.794%   $209.2201   $209.22   $209.20   $209.20  
  Purchase #6 $33.67   6.615%   $35.8973   $35.90   $35.90   $35.90  
  Purchase #7 $245.31   6.180%   $260.4702   $260.47   $260.45   $260.50  
  7 purchase totals = $1,018.67       $1,074.3056   $1,074.31   $1,074.25   $1,074.40