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	$157.42	13.421%	$178.5473	$178.55	$178.55	$178.50
Purchase #2	$245.39	7.161%	$262.9624	$262.96	$262.95	$263.00
Purchase #3	$98.57	4.443%	$102.9495	$102.95	$102.95	$102.90
Purchase #4	$49.64	10.176%	$54.6914	$54.69	$54.70	$54.70
Purchase #5	$241.72	3.603%	$250.4292	$250.43	$250.45	$250.40
Purchase #6	$149.47	13.230%	$169.2449	$169.24	$169.25	$169.20
Purchase #7	$36.69	9.143%	$40.0446	$40.04	$40.05	$40.00
7 purchase totals =	$978.90		$1,058.8693	$1,058.86	$1,058.90	$1,058.70