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	$227.28	12.703%	$256.1514	$256.15	$256.15	$256.20
Purchase #2	$186.27	5.691%	$196.8706	$196.87	$196.85	$196.90
Purchase #3	$24.96	13.303%	$28.2804	$28.28	$28.30	$28.30
Purchase #4	$142.61	5.256%	$150.1056	$150.11	$150.10	$150.10
Purchase #5	$109.33	8.388%	$118.5006	$118.50	$118.50	$118.50
Purchase #6	$84.47	7.641%	$90.9244	$90.92	$90.90	$90.90
Purchase #7	$59.28	9.668%	$65.0112	$65.01	$65.00	$65.00
7 purchase totals =	$834.20		$905.8442	$905.84	$905.80	$905.90