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	$151.51	10.819%	$167.9019	$167.90	$167.90	$167.90
Purchase #2	$171.47	7.765%	$184.7846	$184.78	$184.80	$184.80
Purchase #3	$190.33	12.329%	$213.7958	$213.80	$213.80	$213.80
Purchase #4	$158.27	11.496%	$176.4647	$176.46	$176.45	$176.50
Purchase #5	$229.25	7.811%	$247.1567	$247.16	$247.15	$247.20
Purchase #6	$141.59	9.665%	$155.2747	$155.27	$155.25	$155.30
Purchase #7	$117.83	7.236%	$126.3562	$126.36	$126.35	$126.40
7 purchase totals =	$1,160.25		$1,271.7346	$1,271.73	$1,271.70	$1,271.90