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	$90.65	11.354%	$100.9424	$100.94	$100.95	$100.90
Purchase #2	$53.38	10.595%	$59.0356	$59.04	$59.05	$59.00
Purchase #3	$97.25	6.107%	$103.1891	$103.19	$103.20	$103.20
Purchase #4	$118.41	8.873%	$128.9165	$128.92	$128.90	$128.90
Purchase #5	$121.64	13.486%	$138.0444	$138.04	$138.05	$138.00
Purchase #6	$16.84	11.813%	$18.8293	$18.83	$18.85	$18.80
Purchase #7	$36.61	3.270%	$37.8071	$37.81	$37.80	$37.80
7 purchase totals =	$534.78		$586.7644	$586.77	$586.80	$586.60