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	$40.33	6.266%	$42.8571	$42.86	$42.85	$42.90
Purchase #2	$34.75	3.187%	$35.8575	$35.86	$35.85	$35.90
Purchase #3	$196.66	12.716%	$221.6673	$221.67	$221.65	$221.70
Purchase #4	$127.79	9.584%	$140.0374	$140.04	$140.05	$140.00
Purchase #5	$66.61	5.484%	$70.2629	$70.26	$70.25	$70.30
Purchase #6	$162.49	8.711%	$176.6445	$176.64	$176.65	$176.60
Purchase #7	$118.88	11.700%	$132.789	$132.79	$132.80	$132.80
7 purchase totals =	$747.51		$820.1157	$820.12	$820.10	$820.20