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	$228.56	9.801%	$250.9612	$250.96	$250.95	$251.00
Purchase #2	$214.89	11.536%	$239.6797	$239.68	$239.70	$239.70
Purchase #3	$42.70	13.628%	$48.5192	$48.52	$48.50	$48.50
Purchase #4	$230.28	12.520%	$259.1111	$259.11	$259.10	$259.10
Purchase #5	$134.36	6.368%	$142.916	$142.92	$142.90	$142.90
Purchase #6	$7.61	13.700%	$8.6526	$8.65	$8.65	$8.70
Purchase #7	$60.66	9.582%	$66.4724	$66.47	$66.45	$66.50
7 purchase totals =	$919.06		$1,016.3122	$1,016.31	$1,016.25	$1,016.40