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	$106.28	5.209%	$111.8161	$111.82	$111.80	$111.80
Purchase #2	$216.45	13.802%	$246.3244	$246.32	$246.30	$246.30
Purchase #3	$111.89	10.236%	$123.3431	$123.34	$123.35	$123.30
Purchase #4	$138.41	9.277%	$151.2503	$151.25	$151.25	$151.30
Purchase #5	$24.81	11.829%	$27.7448	$27.74	$27.75	$27.70
Purchase #6	$213.49	6.209%	$226.7456	$226.75	$226.75	$226.70
Purchase #7	$36.43	7.409%	$39.1291	$39.13	$39.15	$39.10
7 purchase totals =	$847.76		$926.3534	$926.35	$926.35	$926.20