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	$113.45	12.725%	$127.8865	$127.89	$127.90	$127.90
Purchase #2	$105.86	6.370%	$112.6033	$112.60	$112.60	$112.60
Purchase #3	$248.48	7.338%	$266.7135	$266.71	$266.70	$266.70
Purchase #4	$246.93	7.500%	$265.4498	$265.45	$265.45	$265.40
Purchase #5	$12.28	4.165%	$12.7915	$12.79	$12.80	$12.80
Purchase #6	$54.65	8.543%	$59.3187	$59.32	$59.30	$59.30
Purchase #7	$157.31	11.843%	$175.9402	$175.94	$175.95	$175.90
7 purchase totals =	$938.96		$1,020.7035	$1,020.70	$1,020.70	$1,020.60