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	$208.94	7.439%	$224.483	$224.48	$224.50	$224.50
Purchase #2	$136.47	4.144%	$142.1253	$142.13	$142.15	$142.10
Purchase #3	$58.78	8.655%	$63.8674	$63.87	$63.85	$63.90
Purchase #4	$62.36	8.256%	$67.5084	$67.51	$67.50	$67.50
Purchase #5	$10.42	8.209%	$11.2754	$11.28	$11.30	$11.30
Purchase #6	$52.27	9.841%	$57.4139	$57.41	$57.40	$57.40
Purchase #7	$75.80	7.506%	$81.4895	$81.49	$81.50	$81.50
7 purchase totals =	$605.04		$648.1629	$648.17	$648.20	$648.20