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 $73.29   4.611%   $76.6694   $76.67   $76.65   $76.70  
  Purchase #2 $122.49   8.338%   $132.7032   $132.70   $132.70   $132.70  
  Purchase #3 $54.39   6.275%   $57.803   $57.80   $57.80   $57.80  
  Purchase #4 $99.58   10.265%   $109.8019   $109.80   $109.80   $109.80  
  Purchase #5 $119.51   4.805%   $125.2525   $125.25   $125.25   $125.30  
  Purchase #6 $149.75   4.177%   $156.0051   $156.01   $156.00   $156.00  
  Purchase #7 $53.43   7.805%   $57.6002   $57.60   $57.60   $57.60  
  7 purchase totals = $672.44       $715.8353   $715.83   $715.80   $715.90