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	$154.96	8.309%	$167.8356	$167.84	$167.85	$167.80
Purchase #2	$134.55	13.819%	$153.1435	$153.14	$153.15	$153.10
Purchase #3	$129.30	6.656%	$137.9062	$137.91	$137.90	$137.90
Purchase #4	$96.65	5.590%	$102.0527	$102.05	$102.05	$102.10
Purchase #5	$143.35	3.547%	$148.4346	$148.43	$148.45	$148.40
Purchase #6	$185.38	3.252%	$191.4086	$191.41	$191.40	$191.40
Purchase #7	$190.78	4.436%	$199.243	$199.24	$199.25	$199.20
7 purchase totals =	$1,034.97		$1,100.0242	$1,100.02	$1,100.05	$1,099.90