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	$125.36	8.569%	$136.1021	$136.10	$136.10	$136.10
Purchase #2	$98.46	11.832%	$110.1098	$110.11	$110.10	$110.10
Purchase #3	$112.29	3.825%	$116.5851	$116.59	$116.60	$116.60
Purchase #4	$64.80	10.337%	$71.4984	$71.50	$71.50	$71.50
Purchase #5	$45.90	13.378%	$52.0405	$52.04	$52.05	$52.00
Purchase #6	$39.62	4.448%	$41.3823	$41.38	$41.40	$41.40
Purchase #7	$235.29	8.664%	$255.6755	$255.68	$255.70	$255.70
7 purchase totals =	$721.72		$783.3937	$783.40	$783.45	$783.40