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	$124.59	13.276%	$141.1306	$141.13	$141.15	$141.10
Purchase #2	$194.51	10.302%	$214.5484	$214.55	$214.55	$214.50
Purchase #3	$141.76	11.739%	$158.4012	$158.40	$158.40	$158.40
Purchase #4	$119.91	3.142%	$123.6776	$123.68	$123.70	$123.70
Purchase #5	$135.53	3.336%	$140.0513	$140.05	$140.05	$140.10
Purchase #6	$96.26	4.754%	$100.8362	$100.84	$100.85	$100.80
Purchase #7	$240.91	3.177%	$248.5637	$248.56	$248.55	$248.60
7 purchase totals =	$1,053.47		$1,127.2090	$1,127.21	$1,127.25	$1,127.20