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	$241.92	11.661%	$270.1303	$270.13	$270.15	$270.10
Purchase #2	$89.88	11.123%	$99.8774	$99.88	$99.90	$99.90
Purchase #3	$96.76	3.244%	$99.8989	$99.90	$99.90	$99.90
Purchase #4	$191.52	13.208%	$216.816	$216.82	$216.80	$216.80
Purchase #5	$117.90	12.214%	$132.3003	$132.30	$132.30	$132.30
Purchase #6	$17.50	12.168%	$19.6294	$19.63	$19.65	$19.60
Purchase #7	$224.79	8.432%	$243.7443	$243.74	$243.75	$243.70
7 purchase totals =	$980.27		$1,082.3966	$1,082.40	$1,082.45	$1,082.30