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	$242.70	4.344%	$253.2429	$253.24	$253.25	$253.20
Purchase #2	$142.43	11.594%	$158.9433	$158.94	$158.95	$158.90
Purchase #3	$73.81	12.413%	$82.972	$82.97	$82.95	$83.00
Purchase #4	$30.78	5.270%	$32.4021	$32.40	$32.40	$32.40
Purchase #5	$109.86	6.343%	$116.8284	$116.83	$116.85	$116.80
Purchase #6	$122.83	8.479%	$133.2448	$133.24	$133.25	$133.20
Purchase #7	$28.92	13.321%	$32.7724	$32.77	$32.75	$32.80
7 purchase totals =	$751.33		$810.4059	$810.39	$810.40	$810.30