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	$90.77	9.398%	$99.3006	$99.30	$99.30	$99.30
Purchase #2	$84.90	7.287%	$91.0867	$91.09	$91.10	$91.10
Purchase #3	$102.27	5.120%	$107.5062	$107.51	$107.50	$107.50
Purchase #4	$92.46	5.470%	$97.5176	$97.52	$97.50	$97.50
Purchase #5	$237.59	4.293%	$247.7897	$247.79	$247.80	$247.80
Purchase #6	$153.89	12.689%	$173.4171	$173.42	$173.40	$173.40
Purchase #7	$120.88	11.623%	$134.9299	$134.93	$134.95	$134.90
7 purchase totals =	$882.76		$951.5478	$951.56	$951.55	$951.50