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	$105.62	11.151%	$117.3977	$117.40	$117.40	$117.40
Purchase #2	$239.94	11.751%	$268.1353	$268.14	$268.15	$268.10
Purchase #3	$33.52	11.124%	$37.2488	$37.25	$37.25	$37.20
Purchase #4	$123.72	6.122%	$131.2941	$131.29	$131.30	$131.30
Purchase #5	$43.66	3.640%	$45.2492	$45.25	$45.25	$45.20
Purchase #6	$103.39	13.573%	$117.4231	$117.42	$117.40	$117.40
Purchase #7	$36.55	4.446%	$38.175	$38.18	$38.20	$38.20
7 purchase totals =	$686.40		$754.9232	$754.93	$754.95	$754.80