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	$27.92	13.280%	$31.6278	$31.63	$31.65	$31.60
Purchase #2	$152.64	13.263%	$172.8846	$172.88	$172.90	$172.90
Purchase #3	$78.60	3.602%	$81.4312	$81.43	$81.45	$81.40
Purchase #4	$210.34	4.309%	$219.4036	$219.40	$219.40	$219.40
Purchase #5	$77.53	13.653%	$88.1152	$88.12	$88.10	$88.10
Purchase #6	$158.43	5.166%	$166.6145	$166.61	$166.60	$166.60
Purchase #7	$205.35	11.649%	$229.2712	$229.27	$229.25	$229.30
7 purchase totals =	$910.81		$989.3481	$989.34	$989.35	$989.30