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	$38.38	5.685%	$40.5619	$40.56	$40.55	$40.60
Purchase #2	$199.35	11.545%	$222.365	$222.37	$222.35	$222.40
Purchase #3	$242.55	12.482%	$272.8251	$272.83	$272.85	$272.80
Purchase #4	$212.80	7.284%	$228.3004	$228.30	$228.30	$228.30
Purchase #5	$128.51	13.278%	$145.5736	$145.57	$145.55	$145.60
Purchase #6	$182.27	12.386%	$204.846	$204.85	$204.85	$204.80
Purchase #7	$179.30	5.485%	$189.1346	$189.13	$189.15	$189.10
7 purchase totals =	$1,183.16		$1,303.6066	$1,303.61	$1,303.60	$1,303.60