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	$48.46	9.564%	$53.0947	$53.09	$53.10	$53.10
Purchase #2	$65.68	12.697%	$74.0194	$74.02	$74.00	$74.00
Purchase #3	$76.56	11.709%	$85.5244	$85.52	$85.50	$85.50
Purchase #4	$138.74	12.667%	$156.3142	$156.31	$156.30	$156.30
Purchase #5	$49.45	7.289%	$53.0544	$53.05	$53.05	$53.10
Purchase #6	$17.90	11.117%	$19.8899	$19.89	$19.90	$19.90
Purchase #7	$150.91	11.821%	$168.7491	$168.75	$168.75	$168.70
7 purchase totals =	$547.70		$610.6461	$610.63	$610.60	$610.60