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	$97.53	3.199%	$100.65	$100.65	$100.65	$100.70
Purchase #2	$193.59	6.531%	$206.2334	$206.23	$206.25	$206.20
Purchase #3	$71.32	12.713%	$80.3869	$80.39	$80.40	$80.40
Purchase #4	$153.72	7.720%	$165.5872	$165.59	$165.60	$165.60
Purchase #5	$198.55	11.483%	$221.3495	$221.35	$221.35	$221.30
Purchase #6	$155.63	11.172%	$173.017	$173.02	$173.00	$173.00
Purchase #7	$218.76	11.565%	$244.0596	$244.06	$244.05	$244.10
7 purchase totals =	$1,089.10		$1,191.2836	$1,191.29	$1,191.30	$1,191.30