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	$82.32	7.574%	$88.5549	$88.55	$88.55	$88.60
Purchase #2	$40.80	13.624%	$46.3586	$46.36	$46.35	$46.40
Purchase #3	$32.25	13.735%	$36.6795	$36.68	$36.70	$36.70
Purchase #4	$97.50	11.799%	$109.004	$109.00	$109.00	$109.00
Purchase #5	$179.28	4.652%	$187.6201	$187.62	$187.60	$187.60
Purchase #6	$33.38	13.308%	$37.8222	$37.82	$37.80	$37.80
Purchase #7	$145.82	12.600%	$164.1933	$164.19	$164.20	$164.20
7 purchase totals =	$611.35		$670.2326	$670.22	$670.20	$670.30