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	$237.27	12.554%	$267.0569	$267.06	$267.05	$267.10
Purchase #2	$39.46	11.149%	$43.8594	$43.86	$43.85	$43.90
Purchase #3	$96.84	12.550%	$108.9934	$108.99	$109.00	$109.00
Purchase #4	$128.35	13.232%	$145.3333	$145.33	$145.35	$145.30
Purchase #5	$112.46	4.419%	$117.4296	$117.43	$117.45	$117.40
Purchase #6	$22.53	13.614%	$25.5972	$25.60	$25.60	$25.60
Purchase #7	$108.82	13.474%	$123.4824	$123.48	$123.50	$123.50
7 purchase totals =	$745.73		$831.7522	$831.75	$831.80	$831.80