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	$182.82	3.183%	$188.6392	$188.64	$188.65	$188.60
Purchase #2	$121.48	10.543%	$134.2876	$134.29	$134.30	$134.30
Purchase #3	$132.32	5.114%	$139.0868	$139.09	$139.10	$139.10
Purchase #4	$213.28	3.667%	$221.101	$221.10	$221.10	$221.10
Purchase #5	$89.50	10.380%	$98.7901	$98.79	$98.80	$98.80
Purchase #6	$40.61	4.129%	$42.2868	$42.29	$42.30	$42.30
Purchase #7	$52.52	4.365%	$54.8125	$54.81	$54.80	$54.80
7 purchase totals =	$832.53		$879.0040	$879.01	$879.05	$879.00