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	$68.76	12.217%	$77.1604	$77.16	$77.15	$77.20
Purchase #2	$41.77	7.587%	$44.9391	$44.94	$44.95	$44.90
Purchase #3	$244.72	10.787%	$271.1179	$271.12	$271.10	$271.10
Purchase #4	$64.34	11.812%	$71.9398	$71.94	$71.95	$71.90
Purchase #5	$51.92	3.269%	$53.6173	$53.62	$53.60	$53.60
Purchase #6	$18.87	10.287%	$20.8112	$20.81	$20.80	$20.80
Purchase #7	$164.39	3.756%	$170.5645	$170.56	$170.55	$170.60
7 purchase totals =	$654.77		$710.1502	$710.15	$710.10	$710.10