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	$90.47	11.281%	$100.6759	$100.68	$100.70	$100.70
Purchase #2	$100.32	11.750%	$112.1076	$112.11	$112.10	$112.10
Purchase #3	$245.97	10.430%	$271.6247	$271.62	$271.60	$271.60
Purchase #4	$17.89	9.132%	$19.5237	$19.52	$19.50	$19.50
Purchase #5	$99.88	8.285%	$108.1551	$108.16	$108.15	$108.20
Purchase #6	$5.41	3.862%	$5.6189	$5.62	$5.60	$5.60
Purchase #7	$62.98	6.723%	$67.2141	$67.21	$67.20	$67.20
7 purchase totals =	$622.92		$684.9200	$684.92	$684.85	$684.90