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	$30.59	11.598%	$34.1378	$34.14	$34.15	$34.10
Purchase #2	$117.59	10.821%	$130.3144	$130.31	$130.30	$130.30
Purchase #3	$37.46	12.693%	$42.2148	$42.21	$42.20	$42.20
Purchase #4	$157.57	8.453%	$170.8894	$170.89	$170.90	$170.90
Purchase #5	$37.27	3.152%	$38.4448	$38.44	$38.45	$38.40
Purchase #6	$175.56	6.252%	$186.536	$186.54	$186.55	$186.50
Purchase #7	$217.67	3.566%	$225.4321	$225.43	$225.45	$225.40
7 purchase totals =	$773.71		$827.9693	$827.96	$828.00	$827.80