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	$71.73	9.810%	$78.7667	$78.77	$78.75	$78.80
Purchase #2	$78.27	8.524%	$84.9417	$84.94	$84.95	$84.90
Purchase #3	$59.49	12.341%	$66.8317	$66.83	$66.85	$66.80
Purchase #4	$247.46	11.136%	$275.0171	$275.02	$275.00	$275.00
Purchase #5	$13.92	11.378%	$15.5038	$15.50	$15.50	$15.50
Purchase #6	$112.42	6.314%	$119.5182	$119.52	$119.50	$119.50
Purchase #7	$18.53	5.825%	$19.6094	$19.61	$19.60	$19.60
7 purchase totals =	$601.82		$660.1886	$660.19	$660.15	$660.10