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	$228.54	6.195%	$242.6981	$242.70	$242.70	$242.70
Purchase #2	$98.90	4.661%	$103.5097	$103.51	$103.50	$103.50
Purchase #3	$79.37	4.148%	$82.6623	$82.66	$82.65	$82.70
Purchase #4	$44.70	11.602%	$49.8861	$49.89	$49.90	$49.90
Purchase #5	$239.90	4.456%	$250.5899	$250.59	$250.60	$250.60
Purchase #6	$61.99	13.118%	$70.1218	$70.12	$70.10	$70.10
Purchase #7	$16.52	12.242%	$18.5424	$18.54	$18.55	$18.50
7 purchase totals =	$769.92		$818.0103	$818.01	$818.00	$818.00