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	$10.35	4.516%	$10.8174	$10.82	$10.80	$10.80
Purchase #2	$137.30	5.410%	$144.7279	$144.73	$144.75	$144.70
Purchase #3	$88.78	8.689%	$96.4941	$96.49	$96.50	$96.50
Purchase #4	$190.42	13.594%	$216.3057	$216.31	$216.30	$216.30
Purchase #5	$110.73	11.773%	$123.7662	$123.77	$123.75	$123.80
Purchase #6	$82.30	11.400%	$91.6822	$91.68	$91.70	$91.70
Purchase #7	$57.61	10.161%	$63.4638	$63.46	$63.45	$63.50
7 purchase totals =	$677.49		$747.2573	$747.26	$747.25	$747.30