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	$142.70	12.204%	$160.1151	$160.12	$160.10	$160.10
Purchase #2	$103.94	10.443%	$114.7945	$114.79	$114.80	$114.80
Purchase #3	$141.81	11.213%	$157.7112	$157.71	$157.70	$157.70
Purchase #4	$131.33	12.436%	$147.6622	$147.66	$147.65	$147.70
Purchase #5	$210.83	5.102%	$221.5865	$221.59	$221.60	$221.60
Purchase #6	$94.52	5.719%	$99.9256	$99.93	$99.95	$99.90
Purchase #7	$205.47	9.744%	$225.491	$225.49	$225.50	$225.50
7 purchase totals =	$1,030.60		$1,127.2861	$1,127.29	$1,127.30	$1,127.30