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	$135.50	11.301%	$150.8129	$150.81	$150.80	$150.80
Purchase #2	$194.25	11.321%	$216.241	$216.24	$216.25	$216.20
Purchase #3	$250.68	6.730%	$267.5508	$267.55	$267.55	$267.60
Purchase #4	$65.65	9.417%	$71.8323	$71.83	$71.85	$71.80
Purchase #5	$51.42	7.841%	$55.4518	$55.45	$55.45	$55.50
Purchase #6	$94.49	9.483%	$103.4505	$103.45	$103.45	$103.50
Purchase #7	$55.59	10.842%	$61.6171	$61.62	$61.60	$61.60
7 purchase totals =	$847.58		$926.9564	$926.95	$926.95	$927.00