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	$183.35	4.373%	$191.3679	$191.37	$191.35	$191.40
Purchase #2	$74.31	10.144%	$81.848	$81.85	$81.85	$81.80
Purchase #3	$122.50	13.857%	$139.4748	$139.47	$139.45	$139.50
Purchase #4	$31.40	3.290%	$32.4331	$32.43	$32.45	$32.40
Purchase #5	$97.46	3.470%	$100.8419	$100.84	$100.85	$100.80
Purchase #6	$142.30	4.740%	$149.045	$149.05	$149.05	$149.00
Purchase #7	$194.89	5.280%	$205.1802	$205.18	$205.20	$205.20
7 purchase totals =	$846.21		$900.1909	$900.19	$900.20	$900.10