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	$102.67	13.851%	$116.8908	$116.89	$116.90	$116.90
Purchase #2	$95.41	5.603%	$100.7558	$100.76	$100.75	$100.80
Purchase #3	$98.60	7.647%	$106.1399	$106.14	$106.15	$106.10
Purchase #4	$14.86	9.670%	$16.297	$16.30	$16.30	$16.30
Purchase #5	$75.39	10.312%	$83.1642	$83.16	$83.15	$83.20
Purchase #6	$75.77	6.594%	$80.7663	$80.77	$80.75	$80.80
Purchase #7	$49.55	10.139%	$54.5739	$54.57	$54.55	$54.60
7 purchase totals =	$512.25		$558.5879	$558.59	$558.55	$558.70