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	$242.84	12.369%	$272.8769	$272.88	$272.90	$272.90
Purchase #2	$240.72	7.713%	$259.2867	$259.29	$259.30	$259.30
Purchase #3	$104.61	6.729%	$111.6492	$111.65	$111.65	$111.60
Purchase #4	$90.72	11.410%	$101.0712	$101.07	$101.05	$101.10
Purchase #5	$20.73	6.355%	$22.0474	$22.05	$22.05	$22.00
Purchase #6	$150.35	5.565%	$158.717	$158.72	$158.70	$158.70
Purchase #7	$114.70	13.700%	$130.4139	$130.41	$130.40	$130.40
7 purchase totals =	$964.67		$1,056.0623	$1,056.07	$1,056.05	$1,056.00