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	$91.68	13.436%	$103.9981	$104.00	$104.00	$104.00
Purchase #2	$160.30	4.499%	$167.5119	$167.51	$167.50	$167.50
Purchase #3	$204.89	10.839%	$227.098	$227.10	$227.10	$227.10
Purchase #4	$96.48	13.103%	$109.1218	$109.12	$109.10	$109.10
Purchase #5	$103.92	3.402%	$107.4554	$107.46	$107.45	$107.50
Purchase #6	$244.45	8.127%	$264.3165	$264.32	$264.30	$264.30
Purchase #7	$95.37	4.434%	$99.5987	$99.60	$99.60	$99.60
7 purchase totals =	$997.09		$1,079.1004	$1,079.11	$1,079.05	$1,079.10