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	$9.25	8.191%	$10.0077	$10.01	$10.00	$10.00
Purchase #2	$200.94	9.466%	$219.961	$219.96	$219.95	$220.00
Purchase #3	$98.90	12.781%	$111.5404	$111.54	$111.55	$111.50
Purchase #4	$59.36	6.169%	$63.0219	$63.02	$63.00	$63.00
Purchase #5	$6.63	3.598%	$6.8685	$6.87	$6.85	$6.90
Purchase #6	$174.66	4.526%	$182.5651	$182.57	$182.55	$182.60
Purchase #7	$39.90	13.444%	$45.2642	$45.26	$45.25	$45.30
7 purchase totals =	$589.64		$639.2288	$639.23	$639.15	$639.30