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	$110.70	11.117%	$123.0065	$123.01	$123.00	$123.00
Purchase #2	$89.84	7.261%	$96.3633	$96.36	$96.35	$96.40
Purchase #3	$126.26	11.612%	$140.9213	$140.92	$140.90	$140.90
Purchase #4	$28.68	12.844%	$32.3637	$32.36	$32.35	$32.40
Purchase #5	$83.93	9.699%	$92.0704	$92.07	$92.05	$92.10
Purchase #6	$214.28	9.404%	$234.4309	$234.43	$234.45	$234.40
Purchase #7	$235.32	10.291%	$259.5368	$259.54	$259.55	$259.50
7 purchase totals =	$889.01		$978.6929	$978.69	$978.65	$978.70