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	$48.41	12.518%	$54.47	$54.47	$54.45	$54.50
Purchase #2	$137.40	10.443%	$151.7487	$151.75	$151.75	$151.70
Purchase #3	$135.38	13.215%	$153.2705	$153.27	$153.25	$153.30
Purchase #4	$15.71	8.221%	$17.0015	$17.00	$17.00	$17.00
Purchase #5	$155.61	10.240%	$171.5445	$171.54	$171.55	$171.50
Purchase #6	$41.82	9.512%	$45.7979	$45.80	$45.80	$45.80
Purchase #7	$242.67	7.321%	$260.4359	$260.44	$260.45	$260.40
7 purchase totals =	$777.00		$854.2690	$854.27	$854.25	$854.20