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	$166.93	7.795%	$179.9422	$179.94	$179.95	$179.90
Purchase #2	$53.30	5.245%	$56.0956	$56.10	$56.10	$56.10
Purchase #3	$69.98	3.248%	$72.253	$72.25	$72.25	$72.30
Purchase #4	$158.39	13.584%	$179.9057	$179.91	$179.90	$179.90
Purchase #5	$143.76	3.262%	$148.4495	$148.45	$148.45	$148.40
Purchase #6	$36.85	12.873%	$41.5937	$41.59	$41.60	$41.60
Purchase #7	$190.96	9.791%	$209.6569	$209.66	$209.65	$209.70
7 purchase totals =	$820.17		$887.8966	$887.90	$887.90	$887.90