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	$50.39	4.274%	$52.5437	$52.54	$52.55	$52.50
Purchase #2	$128.31	10.386%	$141.6363	$141.64	$141.65	$141.60
Purchase #3	$193.49	10.204%	$213.2337	$213.23	$213.25	$213.20
Purchase #4	$69.61	5.591%	$73.5019	$73.50	$73.50	$73.50
Purchase #5	$26.89	7.344%	$28.8648	$28.86	$28.85	$28.90
Purchase #6	$148.52	12.311%	$166.8043	$166.80	$166.80	$166.80
Purchase #7	$117.61	5.419%	$123.9833	$123.98	$124.00	$124.00
7 purchase totals =	$734.82		$800.5680	$800.55	$800.60	$800.50