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	$17.43	7.484%	$18.7345	$18.73	$18.75	$18.70
Purchase #2	$99.86	10.739%	$110.584	$110.58	$110.60	$110.60
Purchase #3	$81.66	10.445%	$90.1894	$90.19	$90.20	$90.20
Purchase #4	$220.72	11.244%	$245.5378	$245.54	$245.55	$245.50
Purchase #5	$83.73	6.812%	$89.4337	$89.43	$89.45	$89.40
Purchase #6	$210.52	3.133%	$217.1156	$217.12	$217.10	$217.10
Purchase #7	$121.78	8.777%	$132.4686	$132.47	$132.45	$132.50
7 purchase totals =	$835.70		$904.0636	$904.06	$904.10	$904.00