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	$127.95	9.196%	$139.7163	$139.72	$139.70	$139.70
Purchase #2	$42.51	6.483%	$45.2659	$45.27	$45.25	$45.30
Purchase #3	$175.45	10.141%	$193.2424	$193.24	$193.25	$193.20
Purchase #4	$53.80	4.199%	$56.0591	$56.06	$56.05	$56.10
Purchase #5	$164.77	4.796%	$172.6724	$172.67	$172.65	$172.70
Purchase #6	$63.80	12.606%	$71.8426	$71.84	$71.85	$71.80
Purchase #7	$55.37	4.336%	$57.7708	$57.77	$57.75	$57.80
7 purchase totals =	$683.65		$736.5695	$736.57	$736.50	$736.60