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	$155.66	6.199%	$165.3094	$165.31	$165.30	$165.30
Purchase #2	$249.84	4.826%	$261.8973	$261.90	$261.90	$261.90
Purchase #3	$220.83	10.758%	$244.5869	$244.59	$244.60	$244.60
Purchase #4	$221.54	13.657%	$251.7957	$251.80	$251.80	$251.80
Purchase #5	$123.52	11.335%	$137.521	$137.52	$137.50	$137.50
Purchase #6	$38.76	12.329%	$43.5387	$43.54	$43.55	$43.50
Purchase #7	$151.47	3.800%	$157.2259	$157.23	$157.25	$157.20
7 purchase totals =	$1,161.62		$1,261.8749	$1,261.89	$1,261.90	$1,261.80