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	$8.51	6.267%	$9.0433	$9.04	$9.05	$9.00
Purchase #2	$55.86	6.720%	$59.6138	$59.61	$59.60	$59.60
Purchase #3	$76.90	7.438%	$82.6198	$82.62	$82.60	$82.60
Purchase #4	$29.66	9.530%	$32.4866	$32.49	$32.50	$32.50
Purchase #5	$110.50	12.123%	$123.8959	$123.90	$123.90	$123.90
Purchase #6	$100.44	6.638%	$107.1072	$107.11	$107.10	$107.10
Purchase #7	$17.49	3.322%	$18.071	$18.07	$18.05	$18.10
7 purchase totals =	$399.36		$432.8376	$432.84	$432.80	$432.80