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	$250.45	5.282%	$263.6788	$263.68	$263.70	$263.70
Purchase #2	$144.92	10.487%	$160.1178	$160.12	$160.10	$160.10
Purchase #3	$169.58	10.588%	$187.5351	$187.54	$187.55	$187.50
Purchase #4	$54.89	8.801%	$59.7209	$59.72	$59.70	$59.70
Purchase #5	$77.74	10.153%	$85.6329	$85.63	$85.65	$85.60
Purchase #6	$222.64	3.578%	$230.6061	$230.61	$230.60	$230.60
Purchase #7	$169.54	13.172%	$191.8718	$191.87	$191.85	$191.90
7 purchase totals =	$1,089.76		$1,179.1634	$1,179.17	$1,179.15	$1,179.10