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	$17.52	4.268%	$18.2678	$18.27	$18.25	$18.30
Purchase #2	$146.81	7.247%	$157.4493	$157.45	$157.45	$157.40
Purchase #3	$198.56	4.261%	$207.0206	$207.02	$207.00	$207.00
Purchase #4	$206.77	3.747%	$214.5177	$214.52	$214.50	$214.50
Purchase #5	$169.71	10.808%	$188.0523	$188.05	$188.05	$188.10
Purchase #6	$82.47	10.483%	$91.1153	$91.12	$91.10	$91.10
Purchase #7	$113.89	12.289%	$127.8859	$127.89	$127.90	$127.90
7 purchase totals =	$935.73		$1,004.3089	$1,004.32	$1,004.25	$1,004.30