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	$156.76	5.733%	$165.7471	$165.75	$165.75	$165.70
Purchase #2	$76.85	4.146%	$80.0362	$80.04	$80.05	$80.00
Purchase #3	$180.28	6.283%	$191.607	$191.61	$191.60	$191.60
Purchase #4	$78.83	5.372%	$83.0647	$83.06	$83.05	$83.10
Purchase #5	$107.29	10.297%	$118.3377	$118.34	$118.35	$118.30
Purchase #6	$42.48	10.451%	$46.9196	$46.92	$46.90	$46.90
Purchase #7	$14.34	6.399%	$15.2576	$15.26	$15.25	$15.30
7 purchase totals =	$656.83		$700.9699	$700.98	$700.95	$700.90