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	$80.39	12.623%	$90.5376	$90.54	$90.55	$90.50
Purchase #2	$111.40	8.181%	$120.5136	$120.51	$120.50	$120.50
Purchase #3	$181.28	13.513%	$205.7764	$205.78	$205.80	$205.80
Purchase #4	$195.28	5.280%	$205.5908	$205.59	$205.60	$205.60
Purchase #5	$99.73	5.819%	$105.5333	$105.53	$105.55	$105.50
Purchase #6	$240.34	7.719%	$258.8918	$258.89	$258.90	$258.90
Purchase #7	$216.81	3.779%	$225.0032	$225.00	$225.00	$225.00
7 purchase totals =	$1,125.23		$1,211.8467	$1,211.84	$1,211.90	$1,211.80