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	$111.91	6.835%	$119.559	$119.56	$119.55	$119.60
Purchase #2	$76.63	8.256%	$82.9566	$82.96	$82.95	$83.00
Purchase #3	$102.50	5.632%	$108.2728	$108.27	$108.25	$108.30
Purchase #4	$78.80	4.552%	$82.387	$82.39	$82.40	$82.40
Purchase #5	$129.85	13.553%	$147.4486	$147.45	$147.45	$147.40
Purchase #6	$166.97	12.719%	$188.2069	$188.21	$188.20	$188.20
Purchase #7	$48.87	6.369%	$51.9825	$51.98	$52.00	$52.00
7 purchase totals =	$715.53		$780.8134	$780.82	$780.80	$780.90