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	$27.55	13.651%	$31.3109	$31.31	$31.30	$31.30
Purchase #2	$101.59	10.384%	$112.1391	$112.14	$112.15	$112.10
Purchase #3	$83.70	13.343%	$94.8681	$94.87	$94.85	$94.90
Purchase #4	$165.84	12.127%	$185.9514	$185.95	$185.95	$186.00
Purchase #5	$45.64	6.548%	$48.6285	$48.63	$48.65	$48.60
Purchase #6	$222.45	9.679%	$243.9809	$243.98	$244.00	$244.00
Purchase #7	$78.25	9.638%	$85.7917	$85.79	$85.80	$85.80
7 purchase totals =	$725.02		$802.6706	$802.67	$802.70	$802.70