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	$11.48	11.322%	$12.7798	$12.78	$12.80	$12.80
Purchase #2	$52.86	6.705%	$56.4043	$56.40	$56.40	$56.40
Purchase #3	$77.58	5.869%	$82.1332	$82.13	$82.15	$82.10
Purchase #4	$202.58	11.697%	$226.2758	$226.28	$226.30	$226.30
Purchase #5	$93.69	6.300%	$99.5925	$99.59	$99.60	$99.60
Purchase #6	$135.51	4.519%	$141.6337	$141.63	$141.65	$141.60
Purchase #7	$39.53	5.656%	$41.7658	$41.77	$41.75	$41.80
7 purchase totals =	$613.23		$660.5851	$660.58	$660.65	$660.60