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	$81.92	4.223%	$85.3795	$85.38	$85.40	$85.40
Purchase #2	$72.26	11.694%	$80.7101	$80.71	$80.70	$80.70
Purchase #3	$239.72	10.468%	$264.8139	$264.81	$264.80	$264.80
Purchase #4	$164.35	4.147%	$171.1656	$171.17	$171.15	$171.20
Purchase #5	$24.35	13.564%	$27.6528	$27.65	$27.65	$27.70
Purchase #6	$217.57	7.627%	$234.1641	$234.16	$234.15	$234.20
Purchase #7	$202.75	6.683%	$216.2998	$216.30	$216.30	$216.30
7 purchase totals =	$1,002.92		$1,080.1858	$1,080.18	$1,080.15	$1,080.30