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	$71.25	12.339%	$80.0415	$80.04	$80.05	$80.00
Purchase #2	$156.94	3.106%	$161.8146	$161.81	$161.80	$161.80
Purchase #3	$102.75	8.273%	$111.2505	$111.25	$111.25	$111.30
Purchase #4	$26.88	3.327%	$27.7743	$27.77	$27.75	$27.80
Purchase #5	$102.88	8.667%	$111.7966	$111.80	$111.80	$111.80
Purchase #6	$62.77	3.761%	$65.1308	$65.13	$65.15	$65.10
Purchase #7	$137.39	7.250%	$147.3508	$147.35	$147.35	$147.40
7 purchase totals =	$660.86		$705.1591	$705.15	$705.15	$705.20