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	$7.82	7.452%	$8.4027	$8.40	$8.40	$8.40
Purchase #2	$110.63	8.835%	$120.4042	$120.40	$120.40	$120.40
Purchase #3	$213.98	13.510%	$242.8887	$242.89	$242.90	$242.90
Purchase #4	$53.59	10.334%	$59.128	$59.13	$59.15	$59.10
Purchase #5	$49.77	10.151%	$54.8222	$54.82	$54.80	$54.80
Purchase #6	$63.67	7.727%	$68.5898	$68.59	$68.60	$68.60
Purchase #7	$140.35	11.121%	$155.9583	$155.96	$155.95	$156.00
7 purchase totals =	$639.81		$710.1939	$710.19	$710.20	$710.20