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	$160.96	13.828%	$183.2175	$183.22	$183.20	$183.20
Purchase #2	$206.45	11.849%	$230.9123	$230.91	$230.90	$230.90
Purchase #3	$54.68	13.840%	$62.2477	$62.25	$62.25	$62.20
Purchase #4	$20.35	5.721%	$21.5142	$21.51	$21.50	$21.50
Purchase #5	$21.41	12.677%	$24.1241	$24.12	$24.10	$24.10
Purchase #6	$136.33	11.666%	$152.2343	$152.23	$152.25	$152.20
Purchase #7	$67.95	7.127%	$72.7928	$72.79	$72.80	$72.80
7 purchase totals =	$668.13		$747.0429	$747.03	$747.00	$746.90