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	$116.54	6.386%	$123.9822	$123.98	$124.00	$124.00
Purchase #2	$138.93	6.257%	$147.6229	$147.62	$147.60	$147.60
Purchase #3	$86.95	10.830%	$96.3667	$96.37	$96.35	$96.40
Purchase #4	$95.50	8.119%	$103.2536	$103.25	$103.25	$103.30
Purchase #5	$158.47	8.403%	$171.7862	$171.79	$171.80	$171.80
Purchase #6	$56.37	4.722%	$59.0318	$59.03	$59.05	$59.00
Purchase #7	$11.68	11.142%	$12.9814	$12.98	$13.00	$13.00
7 purchase totals =	$664.44		$715.0248	$715.02	$715.05	$715.10