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	$26.33	7.644%	$28.3427	$28.34	$28.35	$28.30
Purchase #2	$144.75	3.732%	$150.1521	$150.15	$150.15	$150.20
Purchase #3	$179.74	6.707%	$191.7952	$191.80	$191.80	$191.80
Purchase #4	$36.44	5.709%	$38.5204	$38.52	$38.50	$38.50
Purchase #5	$234.35	9.136%	$255.7602	$255.76	$255.75	$255.80
Purchase #6	$29.60	7.641%	$31.8617	$31.86	$31.85	$31.90
Purchase #7	$210.83	9.577%	$231.0212	$231.02	$231.00	$231.00
7 purchase totals =	$862.04		$927.4535	$927.45	$927.40	$927.50