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	$75.90	5.588%	$80.1413	$80.14	$80.15	$80.10
Purchase #2	$121.34	5.141%	$127.5781	$127.58	$127.60	$127.60
Purchase #3	$193.76	8.290%	$209.8227	$209.82	$209.80	$209.80
Purchase #4	$90.25	12.801%	$101.8029	$101.80	$101.80	$101.80
Purchase #5	$163.72	12.852%	$184.7613	$184.76	$184.75	$184.80
Purchase #6	$85.41	5.446%	$90.0614	$90.06	$90.05	$90.10
Purchase #7	$82.56	13.265%	$93.5116	$93.51	$93.50	$93.50
7 purchase totals =	$812.94		$887.6793	$887.67	$887.65	$887.70