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	$109.28	3.141%	$112.7125	$112.71	$112.70	$112.70
Purchase #2	$79.54	13.802%	$90.5181	$90.52	$90.50	$90.50
Purchase #3	$154.50	3.278%	$159.5645	$159.56	$159.55	$159.60
Purchase #4	$135.98	13.855%	$154.82	$154.82	$154.80	$154.80
Purchase #5	$29.89	12.358%	$33.5838	$33.58	$33.60	$33.60
Purchase #6	$242.27	5.562%	$255.7451	$255.75	$255.75	$255.70
Purchase #7	$72.32	12.839%	$81.6052	$81.61	$81.60	$81.60
7 purchase totals =	$823.78		$888.5492	$888.55	$888.50	$888.50