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	$117.93	10.291%	$130.0662	$130.07	$130.05	$130.10
Purchase #2	$126.31	3.656%	$130.9279	$130.93	$130.95	$130.90
Purchase #3	$73.77	12.421%	$82.933	$82.93	$82.95	$82.90
Purchase #4	$113.95	8.500%	$123.6358	$123.64	$123.65	$123.60
Purchase #5	$165.89	11.537%	$185.0287	$185.03	$185.05	$185.00
Purchase #6	$64.82	10.496%	$71.6235	$71.62	$71.60	$71.60
Purchase #7	$51.96	6.606%	$55.3925	$55.39	$55.40	$55.40
7 purchase totals =	$714.63		$779.6076	$779.61	$779.65	$779.50