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	$33.85	8.138%	$36.6047	$36.60	$36.60	$36.60
Purchase #2	$36.87	4.467%	$38.517	$38.52	$38.50	$38.50
Purchase #3	$73.94	7.675%	$79.6149	$79.61	$79.60	$79.60
Purchase #4	$163.46	5.413%	$172.3081	$172.31	$172.30	$172.30
Purchase #5	$26.29	10.811%	$29.1322	$29.13	$29.15	$29.10
Purchase #6	$103.32	4.801%	$108.2804	$108.28	$108.30	$108.30
Purchase #7	$102.53	6.544%	$109.2396	$109.24	$109.25	$109.20
7 purchase totals =	$540.26		$573.6969	$573.69	$573.70	$573.60