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	$242.43	4.273%	$252.789	$252.79	$252.80	$252.80
Purchase #2	$46.58	12.848%	$52.5646	$52.56	$52.55	$52.60
Purchase #3	$103.63	13.384%	$117.4998	$117.50	$117.50	$117.50
Purchase #4	$40.80	12.537%	$45.9151	$45.92	$45.90	$45.90
Purchase #5	$6.77	7.238%	$7.26	$7.26	$7.25	$7.30
Purchase #6	$90.66	10.210%	$99.9164	$99.92	$99.90	$99.90
Purchase #7	$227.67	11.778%	$254.485	$254.49	$254.50	$254.50
7 purchase totals =	$758.54		$830.4299	$830.44	$830.40	$830.50