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	$82.45	8.698%	$89.6215	$89.62	$89.60	$89.60
Purchase #2	$237.26	5.627%	$250.6106	$250.61	$250.60	$250.60
Purchase #3	$123.62	11.472%	$137.8017	$137.80	$137.80	$137.80
Purchase #4	$98.27	8.612%	$106.733	$106.73	$106.75	$106.70
Purchase #5	$23.65	6.532%	$25.1948	$25.19	$25.20	$25.20
Purchase #6	$224.68	13.627%	$255.2971	$255.30	$255.30	$255.30
Purchase #7	$191.37	4.672%	$200.3108	$200.31	$200.30	$200.30
7 purchase totals =	$981.30		$1,065.5695	$1,065.56	$1,065.55	$1,065.50