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	$136.35	10.386%	$150.5113	$150.51	$150.50	$150.50
Purchase #2	$167.45	11.346%	$186.4489	$186.45	$186.45	$186.40
Purchase #3	$24.32	6.201%	$25.8281	$25.83	$25.85	$25.80
Purchase #4	$95.31	10.429%	$105.2499	$105.25	$105.25	$105.20
Purchase #5	$229.48	7.676%	$247.0949	$247.09	$247.10	$247.10
Purchase #6	$118.33	10.131%	$130.318	$130.32	$130.30	$130.30
Purchase #7	$133.52	4.350%	$139.3281	$139.33	$139.35	$139.30
7 purchase totals =	$904.76		$984.7792	$984.78	$984.80	$984.60