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	$244.58	4.389%	$255.3146	$255.31	$255.30	$255.30
Purchase #2	$50.92	9.797%	$55.9086	$55.91	$55.90	$55.90
Purchase #3	$241.54	5.687%	$255.2764	$255.28	$255.30	$255.30
Purchase #4	$123.25	6.708%	$131.5176	$131.52	$131.50	$131.50
Purchase #5	$232.85	11.285%	$259.1271	$259.13	$259.15	$259.10
Purchase #6	$149.80	11.364%	$166.8233	$166.82	$166.80	$166.80
Purchase #7	$57.89	7.525%	$62.2462	$62.25	$62.25	$62.20
7 purchase totals =	$1,100.83		$1,186.2138	$1,186.22	$1,186.20	$1,186.10