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	$171.59	10.184%	$189.0647	$189.06	$189.05	$189.10
Purchase #2	$49.89	13.260%	$56.5054	$56.51	$56.50	$56.50
Purchase #3	$169.30	4.195%	$176.4021	$176.40	$176.40	$176.40
Purchase #4	$198.83	11.847%	$222.3854	$222.39	$222.40	$222.40
Purchase #5	$61.39	7.747%	$66.1459	$66.15	$66.15	$66.10
Purchase #6	$44.98	4.749%	$47.1161	$47.12	$47.10	$47.10
Purchase #7	$21.40	12.828%	$24.1452	$24.15	$24.15	$24.10
7 purchase totals =	$717.38		$781.7648	$781.78	$781.75	$781.70