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	$36.56	10.671%	$40.4613	$40.46	$40.45	$40.50
Purchase #2	$74.41	10.657%	$82.3399	$82.34	$82.35	$82.30
Purchase #3	$49.84	12.619%	$56.1293	$56.13	$56.15	$56.10
Purchase #4	$42.93	11.416%	$47.8309	$47.83	$47.85	$47.80
Purchase #5	$100.89	5.647%	$106.5873	$106.59	$106.60	$106.60
Purchase #6	$241.97	11.380%	$269.5062	$269.51	$269.50	$269.50
Purchase #7	$182.55	12.497%	$205.3633	$205.36	$205.35	$205.40
7 purchase totals =	$729.15		$808.2182	$808.22	$808.25	$808.20