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	$94.30	5.635%	$99.6138	$99.61	$99.60	$99.60
Purchase #2	$79.58	7.426%	$85.4896	$85.49	$85.50	$85.50
Purchase #3	$167.96	6.380%	$178.6758	$178.68	$178.70	$178.70
Purchase #4	$195.63	7.633%	$210.5624	$210.56	$210.55	$210.60
Purchase #5	$231.77	11.789%	$259.0934	$259.09	$259.10	$259.10
Purchase #6	$42.98	13.173%	$48.6418	$48.64	$48.65	$48.60
Purchase #7	$241.98	6.539%	$257.8031	$257.80	$257.80	$257.80
7 purchase totals =	$1,054.20		$1,139.8799	$1,139.87	$1,139.90	$1,139.90