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	$102.30	5.703%	$108.1342	$108.13	$108.15	$108.10
Purchase #2	$148.89	4.314%	$155.3131	$155.31	$155.30	$155.30
Purchase #3	$29.77	7.569%	$32.0233	$32.02	$32.00	$32.00
Purchase #4	$191.82	5.246%	$201.8829	$201.88	$201.90	$201.90
Purchase #5	$150.45	4.308%	$156.9314	$156.93	$156.95	$156.90
Purchase #6	$33.73	12.150%	$37.8282	$37.83	$37.85	$37.80
Purchase #7	$97.39	12.380%	$109.4469	$109.45	$109.45	$109.40
7 purchase totals =	$754.35		$801.5600	$801.55	$801.60	$801.40