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	$234.54	13.769%	$266.8338	$266.83	$266.85	$266.80
Purchase #2	$228.59	11.398%	$254.6447	$254.64	$254.65	$254.60
Purchase #3	$145.80	10.262%	$160.762	$160.76	$160.75	$160.80
Purchase #4	$237.34	7.658%	$255.5155	$255.52	$255.50	$255.50
Purchase #5	$189.36	11.392%	$210.9319	$210.93	$210.95	$210.90
Purchase #6	$84.37	6.693%	$90.0169	$90.02	$90.00	$90.00
Purchase #7	$10.48	3.823%	$10.8807	$10.88	$10.90	$10.90
7 purchase totals =	$1,130.48		$1,249.5855	$1,249.58	$1,249.60	$1,249.50