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	$152.60	4.453%	$159.3953	$159.40	$159.40	$159.40
Purchase #2	$49.31	10.770%	$54.6207	$54.62	$54.60	$54.60
Purchase #3	$34.25	11.652%	$38.2408	$38.24	$38.25	$38.20
Purchase #4	$203.41	3.172%	$209.8622	$209.86	$209.85	$209.90
Purchase #5	$78.66	4.652%	$82.3193	$82.32	$82.30	$82.30
Purchase #6	$41.29	5.568%	$43.589	$43.59	$43.60	$43.60
Purchase #7	$7.65	7.232%	$8.2032	$8.20	$8.20	$8.20
7 purchase totals =	$567.17		$596.2305	$596.23	$596.20	$596.20