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	$17.45	6.770%	$18.6314	$18.63	$18.65	$18.60
Purchase #2	$176.93	3.102%	$182.4184	$182.42	$182.40	$182.40
Purchase #3	$119.63	6.222%	$127.0734	$127.07	$127.05	$127.10
Purchase #4	$117.25	12.486%	$131.8898	$131.89	$131.90	$131.90
Purchase #5	$130.70	9.181%	$142.6996	$142.70	$142.70	$142.70
Purchase #6	$98.68	6.735%	$105.3261	$105.33	$105.35	$105.30
Purchase #7	$35.74	11.381%	$39.8076	$39.81	$39.80	$39.80
7 purchase totals =	$696.38		$747.8463	$747.85	$747.85	$747.80