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	$103.83	5.464%	$109.5033	$109.50	$109.50	$109.50
Purchase #2	$51.27	8.159%	$55.4531	$55.45	$55.45	$55.50
Purchase #3	$146.25	4.120%	$152.2755	$152.28	$152.30	$152.30
Purchase #4	$107.89	13.303%	$122.2426	$122.24	$122.25	$122.20
Purchase #5	$63.33	8.826%	$68.9195	$68.92	$68.90	$68.90
Purchase #6	$77.56	10.465%	$85.6767	$85.68	$85.70	$85.70
Purchase #7	$11.69	13.754%	$13.2978	$13.30	$13.30	$13.30
7 purchase totals =	$561.82		$607.3685	$607.37	$607.40	$607.40