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	$145.28	10.377%	$160.3557	$160.36	$160.35	$160.40
Purchase #2	$88.62	13.224%	$100.3391	$100.34	$100.35	$100.30
Purchase #3	$80.68	12.352%	$90.6456	$90.65	$90.65	$90.60
Purchase #4	$81.60	6.110%	$86.5858	$86.59	$86.60	$86.60
Purchase #5	$106.92	3.629%	$110.8001	$110.80	$110.80	$110.80
Purchase #6	$19.79	4.413%	$20.6633	$20.66	$20.65	$20.70
Purchase #7	$82.82	11.587%	$92.4164	$92.42	$92.40	$92.40
7 purchase totals =	$605.71		$661.8060	$661.82	$661.80	$661.80