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	$138.49	5.120%	$145.5807	$145.58	$145.60	$145.60
Purchase #2	$250.82	6.582%	$267.329	$267.33	$267.35	$267.30
Purchase #3	$83.60	8.537%	$90.7369	$90.74	$90.75	$90.70
Purchase #4	$165.59	13.848%	$188.5209	$188.52	$188.50	$188.50
Purchase #5	$86.60	7.169%	$92.8084	$92.81	$92.80	$92.80
Purchase #6	$100.34	11.848%	$112.2283	$112.23	$112.25	$112.20
Purchase #7	$119.61	13.751%	$136.0576	$136.06	$136.05	$136.10
7 purchase totals =	$945.05		$1,033.2618	$1,033.27	$1,033.30	$1,033.20