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	$21.51	11.658%	$24.0176	$24.02	$24.00	$24.00
Purchase #2	$17.46	5.135%	$18.3566	$18.36	$18.35	$18.40
Purchase #3	$95.26	12.506%	$107.1732	$107.17	$107.15	$107.20
Purchase #4	$71.54	9.693%	$78.4744	$78.47	$78.45	$78.50
Purchase #5	$26.90	6.609%	$28.6778	$28.68	$28.70	$28.70
Purchase #6	$184.86	7.372%	$198.4879	$198.49	$198.50	$198.50
Purchase #7	$172.89	13.498%	$196.2267	$196.23	$196.25	$196.20
7 purchase totals =	$590.42		$651.4142	$651.42	$651.40	$651.50