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	$38.82	4.130%	$40.4233	$40.42	$40.40	$40.40
Purchase #2	$232.52	3.472%	$240.5931	$240.59	$240.60	$240.60
Purchase #3	$216.28	4.554%	$226.1294	$226.13	$226.15	$226.10
Purchase #4	$18.71	3.198%	$19.3083	$19.31	$19.30	$19.30
Purchase #5	$180.99	8.468%	$196.3162	$196.32	$196.30	$196.30
Purchase #6	$89.71	13.874%	$102.1564	$102.16	$102.15	$102.20
Purchase #7	$249.59	4.431%	$260.6493	$260.65	$260.65	$260.60
7 purchase totals =	$1,026.62		$1,085.5760	$1,085.58	$1,085.55	$1,085.50