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	$124.71	3.854%	$129.5163	$129.52	$129.50	$129.50
Purchase #2	$78.27	6.716%	$83.5266	$83.53	$83.55	$83.50
Purchase #3	$35.83	10.104%	$39.4503	$39.45	$39.45	$39.50
Purchase #4	$18.89	9.122%	$20.6131	$20.61	$20.60	$20.60
Purchase #5	$21.44	4.696%	$22.4468	$22.45	$22.45	$22.40
Purchase #6	$209.74	12.476%	$235.9072	$235.91	$235.90	$235.90
Purchase #7	$138.64	8.245%	$150.0709	$150.07	$150.05	$150.10
7 purchase totals =	$627.52		$681.5312	$681.54	$681.50	$681.50