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	$128.83	7.291%	$138.223	$138.22	$138.20	$138.20
Purchase #2	$162.63	5.781%	$172.0316	$172.03	$172.05	$172.00
Purchase #3	$157.86	5.651%	$166.7807	$166.78	$166.80	$166.80
Purchase #4	$231.43	10.570%	$255.8922	$255.89	$255.90	$255.90
Purchase #5	$133.88	13.287%	$151.6686	$151.67	$151.65	$151.70
Purchase #6	$249.55	12.114%	$279.7805	$279.78	$279.80	$279.80
Purchase #7	$246.32	8.814%	$268.0306	$268.03	$268.05	$268.00
7 purchase totals =	$1,310.50		$1,432.4072	$1,432.40	$1,432.45	$1,432.40