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	$129.76	12.702%	$146.2421	$146.24	$146.25	$146.20
Purchase #2	$179.96	11.275%	$200.2505	$200.25	$200.25	$200.30
Purchase #3	$168.65	4.392%	$176.0571	$176.06	$176.05	$176.10
Purchase #4	$161.45	10.745%	$178.7978	$178.80	$178.80	$178.80
Purchase #5	$61.27	7.367%	$65.7838	$65.78	$65.80	$65.80
Purchase #6	$148.46	11.249%	$165.1603	$165.16	$165.15	$165.20
Purchase #7	$131.50	13.405%	$149.1276	$149.13	$149.15	$149.10
7 purchase totals =	$981.05		$1,081.4192	$1,081.42	$1,081.45	$1,081.50