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	$171.85	10.150%	$189.2928	$189.29	$189.30	$189.30
Purchase #2	$45.91	8.221%	$49.6843	$49.68	$49.70	$49.70
Purchase #3	$232.48	9.391%	$254.3122	$254.31	$254.30	$254.30
Purchase #4	$115.27	7.304%	$123.6893	$123.69	$123.70	$123.70
Purchase #5	$117.67	4.732%	$123.2381	$123.24	$123.25	$123.20
Purchase #6	$157.83	5.493%	$166.4996	$166.50	$166.50	$166.50
Purchase #7	$19.52	6.349%	$20.7593	$20.76	$20.75	$20.80
7 purchase totals =	$860.53		$927.4756	$927.47	$927.50	$927.50