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	$83.32	6.556%	$88.7825	$88.78	$88.80	$88.80
Purchase #2	$168.94	10.753%	$187.1061	$187.11	$187.10	$187.10
Purchase #3	$133.93	5.449%	$141.2278	$141.23	$141.25	$141.20
Purchase #4	$53.89	13.361%	$61.0902	$61.09	$61.10	$61.10
Purchase #5	$139.27	5.120%	$146.4006	$146.40	$146.40	$146.40
Purchase #6	$73.68	13.774%	$83.8287	$83.83	$83.85	$83.80
Purchase #7	$246.47	5.347%	$259.6488	$259.65	$259.65	$259.60
7 purchase totals =	$899.50		$968.0847	$968.09	$968.15	$968.00