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	$84.82	6.672%	$90.4792	$90.48	$90.50	$90.50
Purchase #2	$140.55	10.522%	$155.3387	$155.34	$155.35	$155.30
Purchase #3	$25.71	7.356%	$27.6012	$27.60	$27.60	$27.60
Purchase #4	$177.61	12.229%	$199.3299	$199.33	$199.35	$199.30
Purchase #5	$145.71	5.444%	$153.6425	$153.64	$153.65	$153.60
Purchase #6	$180.25	4.110%	$187.6583	$187.66	$187.65	$187.70
Purchase #7	$38.95	5.137%	$40.9509	$40.95	$40.95	$41.00
7 purchase totals =	$793.60		$855.0007	$855.00	$855.05	$855.00