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	$156.88	13.617%	$178.2423	$178.24	$178.25	$178.20
Purchase #2	$37.46	13.747%	$42.6096	$42.61	$42.60	$42.60
Purchase #3	$176.30	6.587%	$187.9129	$187.91	$187.90	$187.90
Purchase #4	$50.77	9.222%	$55.452	$55.45	$55.45	$55.50
Purchase #5	$174.81	12.563%	$196.7714	$196.77	$196.75	$196.80
Purchase #6	$47.76	9.217%	$52.162	$52.16	$52.15	$52.20
Purchase #7	$201.64	8.180%	$218.1342	$218.13	$218.15	$218.10
7 purchase totals =	$845.62		$931.2844	$931.27	$931.25	$931.30