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	$24.25	12.492%	$27.2793	$27.28	$27.30	$27.30
Purchase #2	$83.47	3.676%	$86.5384	$86.54	$86.55	$86.50
Purchase #3	$75.57	4.281%	$78.8052	$78.81	$78.80	$78.80
Purchase #4	$61.86	9.284%	$67.6031	$67.60	$67.60	$67.60
Purchase #5	$177.90	3.330%	$183.8241	$183.82	$183.80	$183.80
Purchase #6	$180.47	12.393%	$202.8356	$202.84	$202.85	$202.80
Purchase #7	$131.27	8.565%	$142.5133	$142.51	$142.50	$142.50
7 purchase totals =	$734.79		$789.3990	$789.40	$789.40	$789.30