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	$77.84	9.805%	$85.4722	$85.47	$85.45	$85.50
Purchase #2	$51.50	5.121%	$54.1373	$54.14	$54.15	$54.10
Purchase #3	$76.66	13.861%	$87.2858	$87.29	$87.30	$87.30
Purchase #4	$83.84	6.421%	$89.2234	$89.22	$89.20	$89.20
Purchase #5	$249.99	5.821%	$264.5419	$264.54	$264.55	$264.50
Purchase #6	$118.58	9.471%	$129.8107	$129.81	$129.80	$129.80
Purchase #7	$175.87	7.231%	$188.5872	$188.59	$188.60	$188.60
7 purchase totals =	$834.28		$899.0585	$899.06	$899.05	$899.00