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	$107.38	12.551%	$120.8573	$120.86	$120.85	$120.90
Purchase #2	$190.31	5.183%	$200.1738	$200.17	$200.15	$200.20
Purchase #3	$149.64	9.776%	$164.2688	$164.27	$164.25	$164.30
Purchase #4	$162.78	12.299%	$182.8003	$182.80	$182.80	$182.80
Purchase #5	$205.61	3.522%	$212.8516	$212.85	$212.85	$212.90
Purchase #6	$58.31	12.452%	$65.5708	$65.57	$65.55	$65.60
Purchase #7	$141.62	6.722%	$151.1397	$151.14	$151.15	$151.10
7 purchase totals =	$1,015.65		$1,097.6623	$1,097.66	$1,097.60	$1,097.80