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	$85.33	5.251%	$89.8107	$89.81	$89.80	$89.80
Purchase #2	$124.33	6.823%	$132.813	$132.81	$132.80	$132.80
Purchase #3	$134.96	11.861%	$150.9676	$150.97	$150.95	$151.00
Purchase #4	$195.37	13.731%	$222.1963	$222.20	$222.20	$222.20
Purchase #5	$144.93	12.367%	$162.8535	$162.85	$162.85	$162.90
Purchase #6	$144.84	7.187%	$155.2497	$155.25	$155.25	$155.20
Purchase #7	$162.40	13.325%	$184.0398	$184.04	$184.05	$184.00
7 purchase totals =	$992.16		$1,097.9306	$1,097.93	$1,097.90	$1,097.90