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	$18.86	8.505%	$20.464	$20.46	$20.45	$20.50
Purchase #2	$78.69	13.709%	$89.4776	$89.48	$89.50	$89.50
Purchase #3	$115.90	6.658%	$123.6166	$123.62	$123.60	$123.60
Purchase #4	$162.77	7.737%	$175.3635	$175.36	$175.35	$175.40
Purchase #5	$165.77	4.224%	$172.7721	$172.77	$172.75	$172.80
Purchase #6	$157.90	3.457%	$163.3586	$163.36	$163.35	$163.40
Purchase #7	$54.94	11.330%	$61.1647	$61.16	$61.15	$61.20
7 purchase totals =	$754.83		$806.2171	$806.21	$806.15	$806.40