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	$231.90	5.831%	$245.4221	$245.42	$245.40	$245.40
Purchase #2	$7.90	11.325%	$8.7947	$8.79	$8.80	$8.80
Purchase #3	$156.82	11.259%	$174.4764	$174.48	$174.50	$174.50
Purchase #4	$212.63	5.301%	$223.9015	$223.90	$223.90	$223.90
Purchase #5	$175.52	9.105%	$191.5011	$191.50	$191.50	$191.50
Purchase #6	$157.29	12.355%	$176.7232	$176.72	$176.70	$176.70
Purchase #7	$127.84	13.510%	$145.1112	$145.11	$145.10	$145.10
7 purchase totals =	$1,069.90		$1,165.9302	$1,165.92	$1,165.90	$1,165.90