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	$18.85	10.337%	$20.7985	$20.80	$20.80	$20.80
Purchase #2	$157.81	9.502%	$172.8051	$172.81	$172.80	$172.80
Purchase #3	$54.81	4.167%	$57.0939	$57.09	$57.10	$57.10
Purchase #4	$194.48	8.103%	$210.2387	$210.24	$210.25	$210.20
Purchase #5	$53.67	3.572%	$55.5871	$55.59	$55.60	$55.60
Purchase #6	$30.91	4.386%	$32.2657	$32.27	$32.25	$32.30
Purchase #7	$96.48	7.364%	$103.5848	$103.58	$103.60	$103.60
7 purchase totals =	$607.01		$652.3738	$652.38	$652.40	$652.40