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	$78.71	12.379%	$88.4535	$88.45	$88.45	$88.50
Purchase #2	$26.64	8.722%	$28.9635	$28.96	$28.95	$29.00
Purchase #3	$90.72	8.129%	$98.0946	$98.09	$98.10	$98.10
Purchase #4	$85.62	6.604%	$91.2743	$91.27	$91.25	$91.30
Purchase #5	$118.61	4.391%	$123.8182	$123.82	$123.80	$123.80
Purchase #6	$249.72	7.594%	$268.6837	$268.68	$268.70	$268.70
Purchase #7	$155.34	4.312%	$162.0383	$162.04	$162.05	$162.00
7 purchase totals =	$805.36		$861.3261	$861.31	$861.30	$861.40