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	$25.68	10.520%	$28.3815	$28.38	$28.40	$28.40
Purchase #2	$190.29	12.271%	$213.6405	$213.64	$213.65	$213.60
Purchase #3	$159.37	6.168%	$169.1999	$169.20	$169.20	$169.20
Purchase #4	$118.79	11.374%	$132.3012	$132.30	$132.30	$132.30
Purchase #5	$206.97	6.812%	$221.0688	$221.07	$221.05	$221.10
Purchase #6	$230.78	11.527%	$257.382	$257.38	$257.40	$257.40
Purchase #7	$70.94	10.201%	$78.1766	$78.18	$78.20	$78.20
7 purchase totals =	$1,002.82		$1,100.1505	$1,100.15	$1,100.20	$1,100.20