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	$41.51	13.762%	$47.2226	$47.22	$47.20	$47.20
Purchase #2	$238.81	10.712%	$264.3913	$264.39	$264.40	$264.40
Purchase #3	$150.85	12.577%	$169.8224	$169.82	$169.80	$169.80
Purchase #4	$73.52	9.120%	$80.225	$80.23	$80.25	$80.20
Purchase #5	$167.88	6.161%	$178.2231	$178.22	$178.20	$178.20
Purchase #6	$14.85	6.849%	$15.8671	$15.87	$15.85	$15.90
Purchase #7	$91.50	8.804%	$99.5557	$99.56	$99.55	$99.60
7 purchase totals =	$778.92		$855.3072	$855.31	$855.25	$855.30