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	$50.95	8.706%	$55.3857	$55.39	$55.40	$55.40
Purchase #2	$36.43	6.739%	$38.885	$38.89	$38.90	$38.90
Purchase #3	$117.79	10.574%	$130.2451	$130.25	$130.25	$130.20
Purchase #4	$101.50	10.169%	$111.8215	$111.82	$111.80	$111.80
Purchase #5	$147.57	3.635%	$152.9342	$152.93	$152.95	$152.90
Purchase #6	$110.25	7.840%	$118.8936	$118.89	$118.90	$118.90
Purchase #7	$193.74	13.137%	$219.1916	$219.19	$219.20	$219.20
7 purchase totals =	$758.23		$827.3567	$827.36	$827.40	$827.30