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	$32.59	4.588%	$34.0852	$34.09	$34.10	$34.10
Purchase #2	$94.61	9.251%	$103.3624	$103.36	$103.35	$103.40
Purchase #3	$172.32	9.332%	$188.4009	$188.40	$188.40	$188.40
Purchase #4	$123.57	10.244%	$136.2285	$136.23	$136.25	$136.20
Purchase #5	$135.43	5.466%	$142.8326	$142.83	$142.85	$142.80
Purchase #6	$29.89	7.244%	$32.0552	$32.06	$32.05	$32.10
Purchase #7	$205.26	12.591%	$231.1043	$231.10	$231.10	$231.10
7 purchase totals =	$793.67		$868.0691	$868.07	$868.10	$868.10