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	$41.83	6.324%	$44.4753	$44.48	$44.50	$44.50
Purchase #2	$90.66	10.550%	$100.2246	$100.22	$100.20	$100.20
Purchase #3	$106.67	5.737%	$112.7897	$112.79	$112.80	$112.80
Purchase #4	$73.62	5.644%	$77.7751	$77.78	$77.80	$77.80
Purchase #5	$87.53	13.480%	$99.329	$99.33	$99.35	$99.30
Purchase #6	$245.46	5.386%	$258.6805	$258.68	$258.70	$258.70
Purchase #7	$173.27	8.275%	$187.6081	$187.61	$187.60	$187.60
7 purchase totals =	$819.04		$880.8823	$880.89	$880.95	$880.90