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	$78.73	13.214%	$89.1334	$89.13	$89.15	$89.10
Purchase #2	$87.59	3.147%	$90.3465	$90.35	$90.35	$90.30
Purchase #3	$211.39	13.857%	$240.6823	$240.68	$240.70	$240.70
Purchase #4	$5.39	10.681%	$5.9657	$5.97	$5.95	$6.00
Purchase #5	$99.42	12.241%	$111.59	$111.59	$111.60	$111.60
Purchase #6	$205.98	4.137%	$214.5014	$214.50	$214.50	$214.50
Purchase #7	$249.37	3.396%	$257.8386	$257.84	$257.85	$257.80
7 purchase totals =	$937.87		$1,010.0579	$1,010.06	$1,010.10	$1,010.00