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	$33.99	10.840%	$37.6745	$37.67	$37.65	$37.70
Purchase #2	$135.93	5.813%	$143.8316	$143.83	$143.85	$143.80
Purchase #3	$54.26	9.250%	$59.2791	$59.28	$59.30	$59.30
Purchase #4	$177.70	9.496%	$194.5744	$194.57	$194.55	$194.60
Purchase #5	$57.74	8.458%	$62.6236	$62.62	$62.60	$62.60
Purchase #6	$52.71	13.640%	$59.8996	$59.90	$59.90	$59.90
Purchase #7	$92.94	10.809%	$102.9859	$102.99	$103.00	$103.00
7 purchase totals =	$605.27		$660.8687	$660.86	$660.85	$660.90