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	$50.60	13.395%	$57.3779	$57.38	$57.40	$57.40
Purchase #2	$90.94	10.418%	$100.4141	$100.41	$100.40	$100.40
Purchase #3	$128.83	10.622%	$142.5143	$142.51	$142.50	$142.50
Purchase #4	$176.27	5.394%	$185.778	$185.78	$185.80	$185.80
Purchase #5	$158.36	10.853%	$175.5468	$175.55	$175.55	$175.50
Purchase #6	$141.56	4.830%	$148.3973	$148.40	$148.40	$148.40
Purchase #7	$213.63	5.253%	$224.852	$224.85	$224.85	$224.90
7 purchase totals =	$960.19		$1,034.8804	$1,034.88	$1,034.90	$1,034.90