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	$75.67	11.562%	$84.419	$84.42	$84.40	$84.40
Purchase #2	$187.82	13.584%	$213.3335	$213.33	$213.35	$213.30
Purchase #3	$34.81	3.172%	$35.9142	$35.91	$35.90	$35.90
Purchase #4	$117.72	8.427%	$127.6403	$127.64	$127.65	$127.60
Purchase #5	$79.45	4.860%	$83.3113	$83.31	$83.30	$83.30
Purchase #6	$97.64	5.388%	$102.9008	$102.90	$102.90	$102.90
Purchase #7	$59.54	11.208%	$66.2132	$66.21	$66.20	$66.20
7 purchase totals =	$652.65		$713.7323	$713.72	$713.70	$713.60