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	$90.58	11.328%	$100.8409	$100.84	$100.85	$100.80
Purchase #2	$154.57	7.827%	$166.6682	$166.67	$166.65	$166.70
Purchase #3	$13.82	8.513%	$14.9965	$15.00	$15.00	$15.00
Purchase #4	$205.81	8.502%	$223.308	$223.31	$223.30	$223.30
Purchase #5	$50.38	3.612%	$52.1997	$52.20	$52.20	$52.20
Purchase #6	$243.60	7.195%	$261.127	$261.13	$261.15	$261.10
Purchase #7	$244.34	11.294%	$271.9358	$271.94	$271.95	$271.90
7 purchase totals =	$1,003.10		$1,091.0761	$1,091.09	$1,091.10	$1,091.00