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	$145.43	12.297%	$163.3135	$163.31	$163.30	$163.30
Purchase #2	$156.93	3.379%	$162.2327	$162.23	$162.25	$162.20
Purchase #3	$93.69	5.763%	$99.0894	$99.09	$99.10	$99.10
Purchase #4	$12.59	6.792%	$13.4451	$13.45	$13.45	$13.40
Purchase #5	$47.96	13.650%	$54.5065	$54.51	$54.50	$54.50
Purchase #6	$88.79	12.476%	$99.8674	$99.87	$99.85	$99.90
Purchase #7	$242.79	13.363%	$275.234	$275.23	$275.25	$275.20
7 purchase totals =	$788.18		$867.6886	$867.69	$867.70	$867.60