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	$85.89	6.701%	$91.6455	$91.65	$91.65	$91.60
Purchase #2	$67.54	4.495%	$70.5759	$70.58	$70.60	$70.60
Purchase #3	$139.86	11.461%	$155.8894	$155.89	$155.90	$155.90
Purchase #4	$60.64	4.329%	$63.2651	$63.27	$63.25	$63.30
Purchase #5	$7.30	11.529%	$8.1416	$8.14	$8.15	$8.10
Purchase #6	$31.52	10.544%	$34.8435	$34.84	$34.85	$34.80
Purchase #7	$234.89	5.680%	$248.2318	$248.23	$248.25	$248.20
7 purchase totals =	$627.64		$672.5928	$672.60	$672.65	$672.50