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	$58.40	4.680%	$61.1331	$61.13	$61.15	$61.10
Purchase #2	$184.59	12.614%	$207.8742	$207.87	$207.85	$207.90
Purchase #3	$129.70	10.671%	$143.5403	$143.54	$143.55	$143.50
Purchase #4	$91.30	9.331%	$99.8192	$99.82	$99.80	$99.80
Purchase #5	$175.44	11.420%	$195.4752	$195.48	$195.50	$195.50
Purchase #6	$29.42	7.587%	$31.6521	$31.65	$31.65	$31.70
Purchase #7	$82.27	11.189%	$91.4752	$91.48	$91.50	$91.50
7 purchase totals =	$751.12		$830.9693	$830.97	$831.00	$831.00