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	$190.33	8.408%	$206.3329	$206.33	$206.35	$206.30
Purchase #2	$186.96	10.790%	$207.133	$207.13	$207.15	$207.10
Purchase #3	$28.37	4.769%	$29.723	$29.72	$29.70	$29.70
Purchase #4	$31.87	6.369%	$33.8998	$33.90	$33.90	$33.90
Purchase #5	$119.35	6.835%	$127.5076	$127.51	$127.50	$127.50
Purchase #6	$71.52	10.391%	$78.9516	$78.95	$78.95	$79.00
Purchase #7	$176.26	11.598%	$196.7026	$196.70	$196.70	$196.70
7 purchase totals =	$804.66		$880.2505	$880.24	$880.25	$880.20