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	$78.52	3.834%	$81.5305	$81.53	$81.55	$81.50
Purchase #2	$74.83	4.446%	$78.1569	$78.16	$78.15	$78.20
Purchase #3	$28.68	13.275%	$32.4873	$32.49	$32.50	$32.50
Purchase #4	$45.74	12.212%	$51.3258	$51.33	$51.35	$51.30
Purchase #5	$218.34	10.837%	$242.0015	$242.00	$242.00	$242.00
Purchase #6	$229.81	11.396%	$255.9991	$256.00	$256.00	$256.00
Purchase #7	$35.56	8.418%	$38.5534	$38.55	$38.55	$38.60
7 purchase totals =	$711.48		$780.0545	$780.06	$780.10	$780.10