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	$179.38	4.719%	$187.8449	$187.84	$187.85	$187.80
Purchase #2	$35.41	13.603%	$40.2268	$40.23	$40.25	$40.20
Purchase #3	$225.64	12.851%	$254.637	$254.64	$254.65	$254.60
Purchase #4	$231.38	9.238%	$252.7549	$252.75	$252.75	$252.80
Purchase #5	$194.69	4.525%	$203.4997	$203.50	$203.50	$203.50
Purchase #6	$207.41	7.681%	$223.3412	$223.34	$223.35	$223.30
Purchase #7	$56.69	5.120%	$59.5925	$59.59	$59.60	$59.60
7 purchase totals =	$1,130.60		$1,221.8970	$1,221.89	$1,221.95	$1,221.80