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 $192.66   5.174%   $202.6282   $202.63   $202.65   $202.60  
  Purchase #2 $167.68   10.821%   $185.8247   $185.82   $185.80   $185.80  
  Purchase #3 $207.47   6.525%   $221.0074   $221.01   $221.00   $221.00  
  Purchase #4 $101.44   7.714%   $109.2651   $109.27   $109.25   $109.30  
  Purchase #5 $118.95   3.121%   $122.6624   $122.66   $122.65   $122.70  
  Purchase #6 $74.25   12.698%   $83.6783   $83.68   $83.70   $83.70  
  Purchase #7 $101.81   6.827%   $108.7606   $108.76   $108.75   $108.80  
  7 purchase totals = $964.26       $1,033.8267   $1,033.83   $1,033.80   $1,033.90