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	$249.85	10.568%	$276.2541	$276.25	$276.25	$276.30
Purchase #2	$125.94	7.380%	$135.2344	$135.23	$135.25	$135.20
Purchase #3	$90.41	11.257%	$100.5875	$100.59	$100.60	$100.60
Purchase #4	$14.59	6.424%	$15.5273	$15.53	$15.55	$15.50
Purchase #5	$55.33	11.104%	$61.4738	$61.47	$61.45	$61.50
Purchase #6	$17.40	8.649%	$18.9049	$18.90	$18.90	$18.90
Purchase #7	$210.57	5.210%	$221.5407	$221.54	$221.55	$221.50
7 purchase totals =	$764.09		$829.5227	$829.51	$829.55	$829.50