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	$52.25	13.868%	$59.496	$59.50	$59.50	$59.50
Purchase #2	$247.27	13.275%	$280.0951	$280.10	$280.10	$280.10
Purchase #3	$152.59	4.144%	$158.9133	$158.91	$158.90	$158.90
Purchase #4	$186.61	4.436%	$194.888	$194.89	$194.90	$194.90
Purchase #5	$151.96	4.758%	$159.1903	$159.19	$159.20	$159.20
Purchase #6	$139.61	7.196%	$149.6563	$149.66	$149.65	$149.70
Purchase #7	$199.30	9.672%	$218.5763	$218.58	$218.60	$218.60
7 purchase totals =	$1,129.59		$1,220.8153	$1,220.83	$1,220.85	$1,220.90