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	$67.63	7.165%	$72.4757	$72.48	$72.50	$72.50
Purchase #2	$111.89	4.418%	$116.8333	$116.83	$116.85	$116.80
Purchase #3	$14.79	10.463%	$16.3375	$16.34	$16.35	$16.30
Purchase #4	$79.65	11.271%	$88.6274	$88.63	$88.65	$88.60
Purchase #5	$104.47	13.732%	$118.8158	$118.82	$118.80	$118.80
Purchase #6	$89.76	13.185%	$101.5949	$101.59	$101.60	$101.60
Purchase #7	$146.93	11.623%	$164.0077	$164.01	$164.00	$164.00
7 purchase totals =	$615.12		$678.6923	$678.70	$678.75	$678.60