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	$250.57	6.373%	$266.5388	$266.54	$266.55	$266.50
Purchase #2	$98.51	6.690%	$105.1003	$105.10	$105.10	$105.10
Purchase #3	$172.60	6.261%	$183.4065	$183.41	$183.40	$183.40
Purchase #4	$55.75	11.841%	$62.3514	$62.35	$62.35	$62.40
Purchase #5	$33.35	13.546%	$37.8676	$37.87	$37.85	$37.90
Purchase #6	$187.38	11.783%	$209.459	$209.46	$209.45	$209.50
Purchase #7	$237.34	7.854%	$255.9807	$255.98	$256.00	$256.00
7 purchase totals =	$1,035.50		$1,120.7043	$1,120.71	$1,120.70	$1,120.80