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	$103.83	11.817%	$116.0996	$116.10	$116.10	$116.10
Purchase #2	$168.70	3.414%	$174.4594	$174.46	$174.45	$174.50
Purchase #3	$82.25	4.272%	$85.7637	$85.76	$85.75	$85.80
Purchase #4	$71.49	5.261%	$75.2511	$75.25	$75.25	$75.30
Purchase #5	$76.54	3.455%	$79.1845	$79.18	$79.20	$79.20
Purchase #6	$45.74	11.286%	$50.9022	$50.90	$50.90	$50.90
Purchase #7	$63.45	12.824%	$71.5868	$71.59	$71.60	$71.60
7 purchase totals =	$612.00		$653.2473	$653.24	$653.25	$653.40