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	$93.26	6.428%	$99.2548	$99.25	$99.25	$99.30
Purchase #2	$29.48	10.103%	$32.4584	$32.46	$32.45	$32.50
Purchase #3	$54.74	3.463%	$56.6356	$56.64	$56.65	$56.60
Purchase #4	$250.32	12.374%	$281.2946	$281.29	$281.30	$281.30
Purchase #5	$71.68	11.155%	$79.6759	$79.68	$79.70	$79.70
Purchase #6	$134.29	8.383%	$145.5475	$145.55	$145.55	$145.50
Purchase #7	$214.82	7.776%	$231.5244	$231.52	$231.50	$231.50
7 purchase totals =	$848.59		$926.3912	$926.39	$926.40	$926.40