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	$29.61	4.349%	$30.8977	$30.90	$30.90	$30.90
Purchase #2	$91.86	5.564%	$96.9711	$96.97	$96.95	$97.00
Purchase #3	$243.38	13.239%	$275.6011	$275.60	$275.60	$275.60
Purchase #4	$235.85	8.484%	$255.8595	$255.86	$255.85	$255.90
Purchase #5	$50.94	13.393%	$57.7624	$57.76	$57.75	$57.80
Purchase #6	$57.44	7.531%	$61.7658	$61.77	$61.75	$61.80
Purchase #7	$61.39	10.395%	$67.7715	$67.77	$67.75	$67.80
7 purchase totals =	$770.47		$846.6291	$846.63	$846.55	$846.80