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	$19.34	12.214%	$21.7022	$21.70	$21.70	$21.70
Purchase #2	$88.60	3.336%	$91.5557	$91.56	$91.55	$91.60
Purchase #3	$36.69	11.337%	$40.8495	$40.85	$40.85	$40.80
Purchase #4	$194.90	12.371%	$219.0111	$219.01	$219.00	$219.00
Purchase #5	$49.81	10.244%	$54.9125	$54.91	$54.90	$54.90
Purchase #6	$158.88	4.307%	$165.723	$165.72	$165.70	$165.70
Purchase #7	$98.42	13.685%	$111.8888	$111.89	$111.90	$111.90
7 purchase totals =	$646.64		$705.6428	$705.64	$705.60	$705.60