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	$83.33	10.741%	$92.2805	$92.28	$92.30	$92.30
Purchase #2	$197.64	13.474%	$224.27	$224.27	$224.25	$224.30
Purchase #3	$72.67	7.792%	$78.3324	$78.33	$78.35	$78.30
Purchase #4	$127.91	11.516%	$142.6401	$142.64	$142.65	$142.60
Purchase #5	$50.74	10.523%	$56.0794	$56.08	$56.10	$56.10
Purchase #6	$236.25	3.527%	$244.5825	$244.58	$244.60	$244.60
Purchase #7	$16.39	9.292%	$17.913	$17.91	$17.90	$17.90
7 purchase totals =	$784.93		$856.0979	$856.09	$856.15	$856.10