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	$231.37	13.765%	$263.2181	$263.22	$263.20	$263.20
Purchase #2	$134.63	13.859%	$153.2884	$153.29	$153.30	$153.30
Purchase #3	$82.39	10.181%	$90.7781	$90.78	$90.80	$90.80
Purchase #4	$121.84	11.856%	$136.2854	$136.29	$136.30	$136.30
Purchase #5	$247.25	9.203%	$270.0044	$270.00	$270.00	$270.00
Purchase #6	$147.79	4.826%	$154.9223	$154.92	$154.90	$154.90
Purchase #7	$153.51	12.668%	$172.9566	$172.96	$172.95	$173.00
7 purchase totals =	$1,118.78		$1,241.4533	$1,241.46	$1,241.45	$1,241.50