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	$24.87	13.689%	$28.2745	$28.27	$28.25	$28.30
Purchase #2	$146.39	10.670%	$162.0098	$162.01	$162.00	$162.00
Purchase #3	$178.44	6.533%	$190.0975	$190.10	$190.10	$190.10
Purchase #4	$45.56	10.525%	$50.3552	$50.36	$50.35	$50.40
Purchase #5	$160.37	9.332%	$175.3357	$175.34	$175.35	$175.30
Purchase #6	$30.35	4.839%	$31.8186	$31.82	$31.80	$31.80
Purchase #7	$128.91	4.331%	$134.4931	$134.49	$134.50	$134.50
7 purchase totals =	$714.89		$772.3844	$772.39	$772.35	$772.40