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	$72.74	8.854%	$79.1804	$79.18	$79.20	$79.20
Purchase #2	$48.78	8.759%	$53.0526	$53.05	$53.05	$53.10
Purchase #3	$116.94	6.162%	$124.1458	$124.15	$124.15	$124.10
Purchase #4	$160.63	4.704%	$168.186	$168.19	$168.20	$168.20
Purchase #5	$19.69	3.633%	$20.4053	$20.41	$20.40	$20.40
Purchase #6	$90.57	4.601%	$94.7371	$94.74	$94.75	$94.70
Purchase #7	$164.82	4.256%	$171.8347	$171.83	$171.85	$171.80
7 purchase totals =	$674.17		$711.5419	$711.55	$711.60	$711.50