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	$139.69	4.262%	$145.6436	$145.64	$145.65	$145.60
Purchase #2	$8.44	12.345%	$9.4819	$9.48	$9.50	$9.50
Purchase #3	$212.34	8.114%	$229.5693	$229.57	$229.55	$229.60
Purchase #4	$134.59	4.666%	$140.87	$140.87	$140.85	$140.90
Purchase #5	$115.48	10.505%	$127.6112	$127.61	$127.60	$127.60
Purchase #6	$57.55	6.797%	$61.4617	$61.46	$61.45	$61.50
Purchase #7	$146.33	3.532%	$151.4984	$151.50	$151.50	$151.50
7 purchase totals =	$814.42		$866.1361	$866.13	$866.10	$866.20