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	$96.32	6.772%	$102.8428	$102.84	$102.85	$102.80
Purchase #2	$193.59	3.166%	$199.7191	$199.72	$199.70	$199.70
Purchase #3	$160.64	3.613%	$166.4439	$166.44	$166.45	$166.40
Purchase #4	$19.86	3.425%	$20.5402	$20.54	$20.55	$20.50
Purchase #5	$9.88	7.732%	$10.6439	$10.64	$10.65	$10.60
Purchase #6	$70.35	11.499%	$78.4395	$78.44	$78.45	$78.40
Purchase #7	$44.50	10.611%	$49.2219	$49.22	$49.20	$49.20
7 purchase totals =	$595.14		$627.8513	$627.84	$627.85	$627.60