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	$141.77	6.214%	$150.5796	$150.58	$150.60	$150.60
Purchase #2	$96.80	12.356%	$108.7606	$108.76	$108.75	$108.80
Purchase #3	$7.48	10.392%	$8.2573	$8.26	$8.25	$8.30
Purchase #4	$112.67	13.198%	$127.5402	$127.54	$127.55	$127.50
Purchase #5	$63.58	7.185%	$68.1482	$68.15	$68.15	$68.10
Purchase #6	$100.65	7.792%	$108.4926	$108.49	$108.50	$108.50
Purchase #7	$53.63	11.386%	$59.7363	$59.74	$59.75	$59.70
7 purchase totals =	$576.58		$631.5148	$631.52	$631.55	$631.50