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	$29.38	11.802%	$32.8474	$32.85	$32.85	$32.80
Purchase #2	$92.64	6.774%	$98.9154	$98.92	$98.90	$98.90
Purchase #3	$33.85	8.564%	$36.7489	$36.75	$36.75	$36.70
Purchase #4	$24.38	11.860%	$27.2715	$27.27	$27.25	$27.30
Purchase #5	$70.69	10.683%	$78.2418	$78.24	$78.25	$78.20
Purchase #6	$147.30	10.429%	$162.6619	$162.66	$162.65	$162.70
Purchase #7	$44.50	8.457%	$48.2634	$48.26	$48.25	$48.30
7 purchase totals =	$442.74		$484.9503	$484.95	$484.90	$484.90