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	$139.90	11.448%	$155.9158	$155.92	$155.90	$155.90
Purchase #2	$243.94	6.116%	$258.8594	$258.86	$258.85	$258.90
Purchase #3	$42.33	13.646%	$48.1064	$48.11	$48.10	$48.10
Purchase #4	$205.31	3.258%	$211.999	$212.00	$212.00	$212.00
Purchase #5	$172.74	10.841%	$191.4667	$191.47	$191.45	$191.50
Purchase #6	$117.39	8.681%	$127.5806	$127.58	$127.60	$127.60
Purchase #7	$41.79	9.154%	$45.6155	$45.62	$45.60	$45.60
7 purchase totals =	$963.40		$1,039.5434	$1,039.56	$1,039.50	$1,039.60