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	$140.88	5.649%	$148.8383	$148.84	$148.85	$148.80
Purchase #2	$89.83	11.163%	$99.8577	$99.86	$99.85	$99.90
Purchase #3	$102.60	6.240%	$109.0022	$109.00	$109.00	$109.00
Purchase #4	$157.27	6.694%	$167.7977	$167.80	$167.80	$167.80
Purchase #5	$47.95	9.173%	$52.3485	$52.35	$52.35	$52.30
Purchase #6	$231.97	9.507%	$254.0234	$254.02	$254.00	$254.00
Purchase #7	$30.46	13.262%	$34.4996	$34.50	$34.50	$34.50
7 purchase totals =	$800.96		$866.3674	$866.37	$866.35	$866.30