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	$223.49	6.829%	$238.7521	$238.75	$238.75	$238.80
Purchase #2	$122.83	13.679%	$139.6319	$139.63	$139.65	$139.60
Purchase #3	$198.55	11.600%	$221.5818	$221.58	$221.60	$221.60
Purchase #4	$97.78	9.515%	$107.0838	$107.08	$107.10	$107.10
Purchase #5	$72.96	12.492%	$82.0742	$82.07	$82.05	$82.10
Purchase #6	$221.90	3.622%	$229.9372	$229.94	$229.95	$229.90
Purchase #7	$50.39	5.653%	$53.2385	$53.24	$53.25	$53.20
7 purchase totals =	$987.90		$1,072.2995	$1,072.29	$1,072.35	$1,072.30