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	$47.85	9.310%	$52.3048	$52.30	$52.30	$52.30
Purchase #2	$195.54	6.565%	$208.3772	$208.38	$208.40	$208.40
Purchase #3	$105.63	12.323%	$118.6468	$118.65	$118.65	$118.60
Purchase #4	$244.53	4.561%	$255.683	$255.68	$255.70	$255.70
Purchase #5	$32.31	12.802%	$36.4463	$36.45	$36.45	$36.40
Purchase #6	$34.32	4.370%	$35.8198	$35.82	$35.80	$35.80
Purchase #7	$135.98	12.630%	$153.1543	$153.15	$153.15	$153.20
7 purchase totals =	$796.16		$860.4322	$860.43	$860.45	$860.40