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	$146.27	9.599%	$160.3105	$160.31	$160.30	$160.30
Purchase #2	$86.80	10.456%	$95.8758	$95.88	$95.90	$95.90
Purchase #3	$237.56	7.351%	$255.023	$255.02	$255.00	$255.00
Purchase #4	$84.98	5.749%	$89.8655	$89.87	$89.85	$89.90
Purchase #5	$104.52	9.370%	$114.3135	$114.31	$114.30	$114.30
Purchase #6	$74.70	4.383%	$77.9741	$77.97	$77.95	$78.00
Purchase #7	$152.48	7.762%	$164.3155	$164.32	$164.30	$164.30
7 purchase totals =	$887.31		$957.6779	$957.68	$957.60	$957.70