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	$94.62	6.523%	$100.7921	$100.79	$100.80	$100.80
Purchase #2	$35.56	5.360%	$37.466	$37.47	$37.45	$37.50
Purchase #3	$17.94	5.773%	$18.9757	$18.98	$19.00	$19.00
Purchase #4	$209.60	9.299%	$229.0907	$229.09	$229.10	$229.10
Purchase #5	$134.84	13.711%	$153.3279	$153.33	$153.35	$153.30
Purchase #6	$31.71	5.554%	$33.4712	$33.47	$33.45	$33.50
Purchase #7	$128.55	8.383%	$139.3263	$139.33	$139.35	$139.30
7 purchase totals =	$652.82		$712.4499	$712.46	$712.50	$712.50