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	$61.32	4.209%	$63.901	$63.90	$63.90	$63.90
Purchase #2	$127.60	13.662%	$145.0327	$145.03	$145.05	$145.00
Purchase #3	$60.61	3.282%	$62.5992	$62.60	$62.60	$62.60
Purchase #4	$19.97	3.448%	$20.6586	$20.66	$20.65	$20.70
Purchase #5	$71.38	11.275%	$79.4281	$79.43	$79.45	$79.40
Purchase #6	$98.40	11.606%	$109.8203	$109.82	$109.80	$109.80
Purchase #7	$164.65	12.224%	$184.7768	$184.78	$184.80	$184.80
7 purchase totals =	$603.93		$666.2167	$666.22	$666.25	$666.20