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	$158.83	12.489%	$178.6663	$178.67	$178.65	$178.70
Purchase #2	$185.89	5.456%	$196.0322	$196.03	$196.05	$196.00
Purchase #3	$238.77	9.120%	$260.5458	$260.55	$260.55	$260.50
Purchase #4	$154.64	8.766%	$168.1957	$168.20	$168.20	$168.20
Purchase #5	$140.74	3.745%	$146.0107	$146.01	$146.00	$146.00
Purchase #6	$135.59	4.429%	$141.5953	$141.60	$141.60	$141.60
Purchase #7	$18.90	10.146%	$20.8176	$20.82	$20.80	$20.80
7 purchase totals =	$1,033.36		$1,111.8636	$1,111.88	$1,111.85	$1,111.80