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	$25.83	6.513%	$27.5123	$27.51	$27.50	$27.50
Purchase #2	$210.60	12.466%	$236.8534	$236.85	$236.85	$236.90
Purchase #3	$199.99	11.722%	$223.4328	$223.43	$223.45	$223.40
Purchase #4	$136.43	8.684%	$148.2776	$148.28	$148.30	$148.30
Purchase #5	$179.90	4.571%	$188.1232	$188.12	$188.10	$188.10
Purchase #6	$211.39	12.822%	$238.4944	$238.49	$238.50	$238.50
Purchase #7	$191.53	12.797%	$216.0401	$216.04	$216.05	$216.00
7 purchase totals =	$1,155.67		$1,278.7338	$1,278.72	$1,278.75	$1,278.70