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	$27.34	7.317%	$29.3405	$29.34	$29.35	$29.30
Purchase #2	$141.87	4.224%	$147.8626	$147.86	$147.85	$147.90
Purchase #3	$50.57	8.710%	$54.9746	$54.97	$54.95	$55.00
Purchase #4	$85.69	13.556%	$97.3061	$97.31	$97.30	$97.30
Purchase #5	$157.66	9.140%	$172.0701	$172.07	$172.05	$172.10
Purchase #6	$158.82	10.729%	$175.8598	$175.86	$175.85	$175.90
Purchase #7	$181.29	8.269%	$196.2809	$196.28	$196.30	$196.30
7 purchase totals =	$803.24		$873.6946	$873.69	$873.65	$873.80