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	$82.79	8.814%	$90.0871	$90.09	$90.10	$90.10
Purchase #2	$98.93	9.792%	$108.6172	$108.62	$108.60	$108.60
Purchase #3	$124.72	5.555%	$131.6482	$131.65	$131.65	$131.60
Purchase #4	$207.47	7.864%	$223.7854	$223.79	$223.80	$223.80
Purchase #5	$248.42	7.191%	$266.2839	$266.28	$266.30	$266.30
Purchase #6	$157.26	8.418%	$170.4981	$170.50	$170.50	$170.50
Purchase #7	$127.56	10.262%	$140.6502	$140.65	$140.65	$140.70
7 purchase totals =	$1,047.15		$1,131.5701	$1,131.58	$1,131.60	$1,131.60