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	$102.72	3.491%	$106.306	$106.31	$106.30	$106.30
Purchase #2	$103.25	6.187%	$109.6381	$109.64	$109.65	$109.60
Purchase #3	$80.87	9.565%	$88.6052	$88.61	$88.60	$88.60
Purchase #4	$99.96	8.705%	$108.6615	$108.66	$108.65	$108.70
Purchase #5	$219.35	9.842%	$240.9384	$240.94	$240.95	$240.90
Purchase #6	$62.50	3.756%	$64.8475	$64.85	$64.85	$64.80
Purchase #7	$112.51	10.108%	$123.8825	$123.88	$123.90	$123.90
7 purchase totals =	$781.16		$842.8792	$842.89	$842.90	$842.80