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	$137.56	4.543%	$143.8094	$143.81	$143.80	$143.80
Purchase #2	$116.64	12.672%	$131.4206	$131.42	$131.40	$131.40
Purchase #3	$112.39	5.174%	$118.2051	$118.21	$118.20	$118.20
Purchase #4	$233.32	4.673%	$244.223	$244.22	$244.20	$244.20
Purchase #5	$5.38	10.800%	$5.961	$5.96	$5.95	$6.00
Purchase #6	$72.66	13.829%	$82.7082	$82.71	$82.70	$82.70
Purchase #7	$174.59	8.609%	$189.6205	$189.62	$189.60	$189.60
7 purchase totals =	$852.54		$915.9478	$915.95	$915.85	$915.90