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	$78.54	13.543%	$89.1767	$89.18	$89.20	$89.20
Purchase #2	$202.78	3.612%	$210.1044	$210.10	$210.10	$210.10
Purchase #3	$39.68	4.665%	$41.5311	$41.53	$41.55	$41.50
Purchase #4	$60.94	7.499%	$65.5099	$65.51	$65.50	$65.50
Purchase #5	$35.56	8.487%	$38.578	$38.58	$38.60	$38.60
Purchase #6	$159.69	7.145%	$171.0999	$171.10	$171.10	$171.10
Purchase #7	$100.54	13.805%	$114.4195	$114.42	$114.40	$114.40
7 purchase totals =	$677.73		$730.4195	$730.42	$730.45	$730.40