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	$111.71	5.799%	$118.1881	$118.19	$118.20	$118.20
Purchase #2	$41.33	8.631%	$44.8972	$44.90	$44.90	$44.90
Purchase #3	$208.59	4.858%	$218.7233	$218.72	$218.70	$218.70
Purchase #4	$19.76	6.624%	$21.0689	$21.07	$21.05	$21.10
Purchase #5	$109.35	12.834%	$123.384	$123.38	$123.40	$123.40
Purchase #6	$231.77	4.702%	$242.6678	$242.67	$242.65	$242.70
Purchase #7	$36.25	10.821%	$40.1726	$40.17	$40.15	$40.20
7 purchase totals =	$758.76		$809.1019	$809.10	$809.05	$809.20