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	$137.37	12.241%	$154.1855	$154.19	$154.20	$154.20
Purchase #2	$50.72	11.118%	$56.359	$56.36	$56.35	$56.40
Purchase #3	$145.73	3.829%	$151.31	$151.31	$151.30	$151.30
Purchase #4	$165.28	7.429%	$177.5587	$177.56	$177.55	$177.60
Purchase #5	$203.94	4.246%	$212.5993	$212.60	$212.60	$212.60
Purchase #6	$37.57	12.760%	$42.3639	$42.36	$42.35	$42.40
Purchase #7	$89.54	6.532%	$95.3888	$95.39	$95.40	$95.40
7 purchase totals =	$830.15		$889.7652	$889.77	$889.75	$889.90