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	$14.97	10.847%	$16.5938	$16.59	$16.60	$16.60
Purchase #2	$224.89	8.598%	$244.226	$244.23	$244.25	$244.20
Purchase #3	$62.46	6.630%	$66.6011	$66.60	$66.60	$66.60
Purchase #4	$29.57	12.600%	$33.2958	$33.30	$33.30	$33.30
Purchase #5	$54.42	4.543%	$56.8923	$56.89	$56.90	$56.90
Purchase #6	$104.57	6.264%	$111.1203	$111.12	$111.10	$111.10
Purchase #7	$129.97	13.419%	$147.4107	$147.41	$147.40	$147.40
7 purchase totals =	$620.85		$676.1400	$676.14	$676.15	$676.10