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	$66.54	11.684%	$74.3145	$74.31	$74.30	$74.30
Purchase #2	$68.53	5.836%	$72.5294	$72.53	$72.55	$72.50
Purchase #3	$32.42	12.429%	$36.4495	$36.45	$36.45	$36.40
Purchase #4	$186.76	9.710%	$204.8944	$204.89	$204.90	$204.90
Purchase #5	$28.31	11.269%	$31.5003	$31.50	$31.50	$31.50
Purchase #6	$68.69	13.544%	$77.9934	$77.99	$78.00	$78.00
Purchase #7	$16.84	12.439%	$18.9347	$18.93	$18.95	$18.90
7 purchase totals =	$468.09		$516.6162	$516.60	$516.65	$516.50