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	$37.48	12.541%	$42.1804	$42.18	$42.20	$42.20
Purchase #2	$112.78	13.205%	$127.6726	$127.67	$127.65	$127.70
Purchase #3	$160.28	6.232%	$170.2686	$170.27	$170.25	$170.30
Purchase #4	$71.96	7.253%	$77.1793	$77.18	$77.20	$77.20
Purchase #5	$100.58	11.538%	$112.1849	$112.18	$112.20	$112.20
Purchase #6	$52.59	7.849%	$56.7178	$56.72	$56.70	$56.70
Purchase #7	$38.52	8.783%	$41.9032	$41.90	$41.90	$41.90
7 purchase totals =	$574.19		$628.1068	$628.10	$628.10	$628.20