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	$124.28	12.734%	$140.1058	$140.11	$140.10	$140.10
Purchase #2	$61.58	9.462%	$67.4067	$67.41	$67.40	$67.40
Purchase #3	$54.75	6.481%	$58.2983	$58.30	$58.30	$58.30
Purchase #4	$24.92	10.351%	$27.4995	$27.50	$27.50	$27.50
Purchase #5	$50.48	7.491%	$54.2615	$54.26	$54.25	$54.30
Purchase #6	$78.85	4.555%	$82.4416	$82.44	$82.45	$82.40
Purchase #7	$91.25	11.618%	$101.8514	$101.85	$101.85	$101.90
7 purchase totals =	$486.11		$531.8648	$531.87	$531.85	$531.90