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	$54.83	13.226%	$62.0818	$62.08	$62.10	$62.10
Purchase #2	$90.74	11.582%	$101.2495	$101.25	$101.25	$101.20
Purchase #3	$178.38	7.111%	$191.0646	$191.06	$191.05	$191.10
Purchase #4	$49.31	5.108%	$51.8288	$51.83	$51.85	$51.80
Purchase #5	$16.44	12.430%	$18.4835	$18.48	$18.50	$18.50
Purchase #6	$9.65	3.219%	$9.9606	$9.96	$9.95	$10.00
Purchase #7	$48.50	13.155%	$54.8802	$54.88	$54.90	$54.90
7 purchase totals =	$447.85		$489.5490	$489.54	$489.60	$489.60