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	$27.60	13.597%	$31.3528	$31.35	$31.35	$31.40
Purchase #2	$238.88	3.214%	$246.5576	$246.56	$246.55	$246.60
Purchase #3	$85.37	10.279%	$94.1452	$94.15	$94.15	$94.10
Purchase #4	$158.86	9.662%	$174.2091	$174.21	$174.20	$174.20
Purchase #5	$174.36	12.569%	$196.2753	$196.28	$196.30	$196.30
Purchase #6	$46.51	9.350%	$50.8587	$50.86	$50.85	$50.90
Purchase #7	$70.85	10.719%	$78.4444	$78.44	$78.45	$78.40
7 purchase totals =	$802.43		$871.8431	$871.85	$871.85	$871.90