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	$120.37	9.807%	$132.1747	$132.17	$132.15	$132.20
Purchase #2	$183.32	11.593%	$204.5723	$204.57	$204.55	$204.60
Purchase #3	$142.91	9.102%	$155.9177	$155.92	$155.90	$155.90
Purchase #4	$93.69	7.202%	$100.4376	$100.44	$100.45	$100.40
Purchase #5	$191.60	11.304%	$213.2585	$213.26	$213.25	$213.30
Purchase #6	$33.93	11.580%	$37.8591	$37.86	$37.85	$37.90
Purchase #7	$54.86	7.724%	$59.0974	$59.10	$59.10	$59.10
7 purchase totals =	$820.68		$903.3173	$903.32	$903.25	$903.40