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	$19.48	6.264%	$20.7002	$20.70	$20.70	$20.70
Purchase #2	$200.51	7.767%	$216.0836	$216.08	$216.10	$216.10
Purchase #3	$10.26	10.275%	$11.3142	$11.31	$11.30	$11.30
Purchase #4	$77.68	6.795%	$82.9584	$82.96	$82.95	$83.00
Purchase #5	$10.72	13.206%	$12.1357	$12.14	$12.15	$12.10
Purchase #6	$12.37	9.587%	$13.5559	$13.56	$13.55	$13.60
Purchase #7	$148.43	13.469%	$168.422	$168.42	$168.40	$168.40
7 purchase totals =	$479.45		$525.1700	$525.17	$525.15	$525.20