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	$49.69	9.598%	$54.4592	$54.46	$54.45	$54.50
Purchase #2	$237.40	12.775%	$267.7279	$267.73	$267.75	$267.70
Purchase #3	$8.44	5.659%	$8.9176	$8.92	$8.90	$8.90
Purchase #4	$50.71	4.806%	$53.1471	$53.15	$53.15	$53.10
Purchase #5	$179.66	4.749%	$188.1921	$188.19	$188.20	$188.20
Purchase #6	$216.72	11.309%	$241.2289	$241.23	$241.25	$241.20
Purchase #7	$88.42	13.453%	$100.3151	$100.32	$100.30	$100.30
7 purchase totals =	$831.04		$913.9879	$914.00	$914.00	$913.90