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	$48.41	11.859%	$54.1509	$54.15	$54.15	$54.20
Purchase #2	$34.91	7.559%	$37.5488	$37.55	$37.55	$37.50
Purchase #3	$230.71	3.546%	$238.891	$238.89	$238.90	$238.90
Purchase #4	$49.33	3.200%	$50.9086	$50.91	$50.90	$50.90
Purchase #5	$211.45	5.553%	$223.1918	$223.19	$223.20	$223.20
Purchase #6	$178.99	9.815%	$196.5579	$196.56	$196.55	$196.60
Purchase #7	$89.47	13.318%	$101.3856	$101.39	$101.40	$101.40
7 purchase totals =	$843.27		$902.6346	$902.64	$902.65	$902.70