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	$132.72	3.358%	$137.1767	$137.18	$137.20	$137.20
Purchase #2	$100.30	7.860%	$108.1836	$108.18	$108.20	$108.20
Purchase #3	$228.36	9.255%	$249.4947	$249.49	$249.50	$249.50
Purchase #4	$86.57	12.852%	$97.696	$97.70	$97.70	$97.70
Purchase #5	$67.74	5.288%	$71.3221	$71.32	$71.30	$71.30
Purchase #6	$173.50	7.157%	$185.9174	$185.92	$185.90	$185.90
Purchase #7	$123.74	3.659%	$128.2676	$128.27	$128.25	$128.30
7 purchase totals =	$912.93		$978.0581	$978.06	$978.05	$978.10