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	$152.54	8.394%	$165.3442	$165.34	$165.35	$165.30
Purchase #2	$220.61	12.503%	$248.1929	$248.19	$248.20	$248.20
Purchase #3	$17.85	12.246%	$20.0359	$20.04	$20.05	$20.00
Purchase #4	$80.72	12.812%	$91.0618	$91.06	$91.05	$91.10
Purchase #5	$158.29	13.580%	$179.7858	$179.79	$179.80	$179.80
Purchase #6	$225.55	5.722%	$238.456	$238.46	$238.45	$238.50
Purchase #7	$130.74	4.355%	$136.4337	$136.43	$136.45	$136.40
7 purchase totals =	$986.30		$1,079.3103	$1,079.31	$1,079.35	$1,079.30