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	$239.64	8.120%	$259.0988	$259.10	$259.10	$259.10
Purchase #2	$137.53	13.872%	$156.6082	$156.61	$156.60	$156.60
Purchase #3	$94.67	11.459%	$105.5182	$105.52	$105.50	$105.50
Purchase #4	$107.64	5.792%	$113.8745	$113.87	$113.85	$113.90
Purchase #5	$16.31	10.446%	$18.0137	$18.01	$18.00	$18.00
Purchase #6	$92.33	10.342%	$101.8788	$101.88	$101.90	$101.90
Purchase #7	$70.33	4.668%	$73.613	$73.61	$73.60	$73.60
7 purchase totals =	$758.45		$828.6052	$828.60	$828.55	$828.60