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	$96.75	13.109%	$109.433	$109.43	$109.45	$109.40
Purchase #2	$226.99	5.207%	$238.8094	$238.81	$238.80	$238.80
Purchase #3	$146.65	7.142%	$157.1237	$157.12	$157.10	$157.10
Purchase #4	$43.47	3.825%	$45.1327	$45.13	$45.15	$45.10
Purchase #5	$142.76	4.216%	$148.7788	$148.78	$148.80	$148.80
Purchase #6	$73.38	10.271%	$80.9169	$80.92	$80.90	$80.90
Purchase #7	$44.45	13.204%	$50.3192	$50.32	$50.30	$50.30
7 purchase totals =	$774.45		$830.5137	$830.51	$830.50	$830.40