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	$64.99	8.441%	$70.4758	$70.48	$70.50	$70.50
Purchase #2	$82.37	11.527%	$91.8648	$91.86	$91.85	$91.90
Purchase #3	$143.95	12.659%	$162.1726	$162.17	$162.15	$162.20
Purchase #4	$11.95	10.165%	$13.1647	$13.16	$13.15	$13.20
Purchase #5	$81.84	4.169%	$85.2519	$85.25	$85.25	$85.30
Purchase #6	$98.69	3.411%	$102.0563	$102.06	$102.05	$102.10
Purchase #7	$89.38	6.868%	$95.5186	$95.52	$95.50	$95.50
7 purchase totals =	$573.17		$620.5047	$620.50	$620.45	$620.70