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	$48.74	3.218%	$50.3085	$50.31	$50.30	$50.30
Purchase #2	$10.79	6.591%	$11.5012	$11.50	$11.50	$11.50
Purchase #3	$205.48	5.372%	$216.5184	$216.52	$216.50	$216.50
Purchase #4	$93.82	6.149%	$99.589	$99.59	$99.60	$99.60
Purchase #5	$240.94	7.615%	$259.2876	$259.29	$259.30	$259.30
Purchase #6	$73.87	7.578%	$79.4679	$79.47	$79.45	$79.50
Purchase #7	$197.61	12.627%	$222.5622	$222.56	$222.55	$222.60
7 purchase totals =	$871.25		$939.2348	$939.24	$939.20	$939.30