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	$90.57	9.803%	$99.4486	$99.45	$99.45	$99.40
Purchase #2	$56.72	10.153%	$62.4788	$62.48	$62.50	$62.50
Purchase #3	$54.81	5.805%	$57.9917	$57.99	$58.00	$58.00
Purchase #4	$78.34	10.675%	$86.7028	$86.70	$86.70	$86.70
Purchase #5	$243.77	8.192%	$263.7396	$263.74	$263.75	$263.70
Purchase #6	$56.98	9.859%	$62.5977	$62.60	$62.60	$62.60
Purchase #7	$46.43	10.446%	$51.2801	$51.28	$51.30	$51.30
7 purchase totals =	$627.62		$684.2393	$684.24	$684.30	$684.20