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	$81.34	11.483%	$90.6803	$90.68	$90.70	$90.70
Purchase #2	$79.60	12.160%	$89.2794	$89.28	$89.30	$89.30
Purchase #3	$37.62	11.216%	$41.8395	$41.84	$41.85	$41.80
Purchase #4	$62.41	6.400%	$66.4042	$66.40	$66.40	$66.40
Purchase #5	$73.73	5.839%	$78.0351	$78.04	$78.05	$78.00
Purchase #6	$33.73	8.229%	$36.5056	$36.51	$36.50	$36.50
Purchase #7	$47.83	5.500%	$50.4607	$50.46	$50.45	$50.50
7 purchase totals =	$416.26		$453.2048	$453.21	$453.25	$453.20