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	$56.27	6.593%	$59.9799	$59.98	$60.00	$60.00
Purchase #2	$228.60	6.415%	$243.2647	$243.26	$243.25	$243.30
Purchase #3	$47.71	7.402%	$51.2415	$51.24	$51.25	$51.20
Purchase #4	$53.48	10.657%	$59.1794	$59.18	$59.20	$59.20
Purchase #5	$217.43	5.406%	$229.1843	$229.18	$229.20	$229.20
Purchase #6	$73.58	12.473%	$82.7576	$82.76	$82.75	$82.80
Purchase #7	$215.48	8.443%	$233.673	$233.67	$233.65	$233.70
7 purchase totals =	$892.55		$959.2804	$959.27	$959.30	$959.40