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	$250.35	11.558%	$279.2855	$279.29	$279.30	$279.30
Purchase #2	$114.83	11.590%	$128.1388	$128.14	$128.15	$128.10
Purchase #3	$137.71	11.453%	$153.4819	$153.48	$153.50	$153.50
Purchase #4	$175.27	5.859%	$185.5391	$185.54	$185.55	$185.50
Purchase #5	$98.83	8.325%	$107.0576	$107.06	$107.05	$107.10
Purchase #6	$106.56	12.213%	$119.5742	$119.57	$119.55	$119.60
Purchase #7	$223.91	7.613%	$240.9563	$240.96	$240.95	$241.00
7 purchase totals =	$1,107.46		$1,214.0334	$1,214.04	$1,214.05	$1,214.10