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	$36.83	13.258%	$41.7129	$41.71	$41.70	$41.70
Purchase #2	$24.44	8.325%	$26.4746	$26.47	$26.45	$26.50
Purchase #3	$57.35	4.455%	$59.9049	$59.90	$59.90	$59.90
Purchase #4	$106.94	9.679%	$117.2907	$117.29	$117.30	$117.30
Purchase #5	$39.83	5.565%	$42.0465	$42.05	$42.05	$42.00
Purchase #6	$219.50	6.250%	$233.2188	$233.22	$233.20	$233.20
Purchase #7	$96.26	3.314%	$99.4501	$99.45	$99.45	$99.50
7 purchase totals =	$581.15		$620.0985	$620.09	$620.05	$620.10