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	$179.78	11.563%	$200.568	$200.57	$200.55	$200.60
Purchase #2	$229.56	11.699%	$256.4162	$256.42	$256.40	$256.40
Purchase #3	$36.77	3.225%	$37.9558	$37.96	$37.95	$38.00
Purchase #4	$56.45	3.135%	$58.2197	$58.22	$58.20	$58.20
Purchase #5	$231.35	13.672%	$262.9802	$262.98	$263.00	$263.00
Purchase #6	$50.94	5.314%	$53.647	$53.65	$53.65	$53.60
Purchase #7	$45.72	9.644%	$50.1292	$50.13	$50.15	$50.10
7 purchase totals =	$830.57		$919.9161	$919.93	$919.90	$919.90