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	$144.94	7.501%	$155.8119	$155.81	$155.80	$155.80
Purchase #2	$160.79	7.870%	$173.4442	$173.44	$173.45	$173.40
Purchase #3	$115.48	12.586%	$130.0143	$130.01	$130.00	$130.00
Purchase #4	$166.88	4.652%	$174.6433	$174.64	$174.65	$174.60
Purchase #5	$79.58	13.246%	$90.1212	$90.12	$90.10	$90.10
Purchase #6	$201.45	13.284%	$228.2106	$228.21	$228.20	$228.20
Purchase #7	$132.27	12.322%	$148.5683	$148.57	$148.55	$148.60
7 purchase totals =	$1,001.39		$1,100.8138	$1,100.80	$1,100.75	$1,100.70