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	$50.68	9.802%	$55.6477	$55.65	$55.65	$55.60
Purchase #2	$68.97	12.830%	$77.8189	$77.82	$77.80	$77.80
Purchase #3	$234.60	10.636%	$259.5521	$259.55	$259.55	$259.60
Purchase #4	$79.92	12.216%	$89.683	$89.68	$89.70	$89.70
Purchase #5	$168.85	9.472%	$184.8435	$184.84	$184.85	$184.80
Purchase #6	$189.72	11.216%	$210.999	$211.00	$211.00	$211.00
Purchase #7	$126.48	9.334%	$138.2856	$138.29	$138.30	$138.30
7 purchase totals =	$919.22		$1,016.8298	$1,016.83	$1,016.85	$1,016.80