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	$9.92	6.219%	$10.5369	$10.54	$10.55	$10.50
Purchase #2	$155.46	4.480%	$162.4246	$162.42	$162.40	$162.40
Purchase #3	$46.82	4.616%	$48.9812	$48.98	$49.00	$49.00
Purchase #4	$201.54	5.445%	$212.5139	$212.51	$212.50	$212.50
Purchase #5	$93.78	7.639%	$100.9439	$100.94	$100.95	$100.90
Purchase #6	$76.30	13.129%	$86.3174	$86.32	$86.30	$86.30
Purchase #7	$147.68	11.812%	$165.124	$165.12	$165.10	$165.10
7 purchase totals =	$731.50		$786.8419	$786.83	$786.80	$786.70