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	$199.35	12.655%	$224.5777	$224.58	$224.60	$224.60
Purchase #2	$79.58	13.677%	$90.4642	$90.46	$90.45	$90.50
Purchase #3	$151.27	13.787%	$172.1256	$172.13	$172.15	$172.10
Purchase #4	$27.30	5.324%	$28.7535	$28.75	$28.75	$28.80
Purchase #5	$243.89	10.464%	$269.4106	$269.41	$269.40	$269.40
Purchase #6	$194.81	9.245%	$212.8202	$212.82	$212.80	$212.80
Purchase #7	$36.78	11.365%	$40.96	$40.96	$40.95	$41.00
7 purchase totals =	$932.98		$1,039.1118	$1,039.11	$1,039.10	$1,039.20