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	$138.93	3.840%	$144.2649	$144.26	$144.25	$144.30
Purchase #2	$69.75	12.675%	$78.5908	$78.59	$78.60	$78.60
Purchase #3	$133.28	6.217%	$141.566	$141.57	$141.55	$141.60
Purchase #4	$223.43	4.427%	$233.3212	$233.32	$233.30	$233.30
Purchase #5	$191.59	13.789%	$218.0083	$218.01	$218.00	$218.00
Purchase #6	$176.98	3.784%	$183.6769	$183.68	$183.70	$183.70
Purchase #7	$206.83	11.644%	$230.9133	$230.91	$230.90	$230.90
7 purchase totals =	$1,140.79		$1,230.3414	$1,230.34	$1,230.30	$1,230.40