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	$78.27	8.779%	$85.1413	$85.14	$85.15	$85.10
Purchase #2	$62.95	6.306%	$66.9196	$66.92	$66.90	$66.90
Purchase #3	$70.58	10.553%	$78.0283	$78.03	$78.05	$78.00
Purchase #4	$154.27	4.200%	$160.7493	$160.75	$160.75	$160.70
Purchase #5	$161.62	11.578%	$180.3324	$180.33	$180.35	$180.30
Purchase #6	$211.96	6.749%	$226.2652	$226.27	$226.25	$226.30
Purchase #7	$71.52	9.803%	$78.5311	$78.53	$78.55	$78.50
7 purchase totals =	$811.17		$875.9672	$875.97	$876.00	$875.80