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	$219.60	13.824%	$249.9575	$249.96	$249.95	$250.00
Purchase #2	$185.97	5.687%	$196.5461	$196.55	$196.55	$196.50
Purchase #3	$101.84	6.777%	$108.7417	$108.74	$108.75	$108.70
Purchase #4	$194.35	11.611%	$216.916	$216.92	$216.90	$216.90
Purchase #5	$141.39	6.792%	$150.9932	$150.99	$151.00	$151.00
Purchase #6	$212.95	4.786%	$223.1418	$223.14	$223.15	$223.10
Purchase #7	$136.46	11.494%	$152.1447	$152.14	$152.15	$152.10
7 purchase totals =	$1,192.56		$1,298.4410	$1,298.44	$1,298.45	$1,298.30