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	$55.76	6.671%	$59.4797	$59.48	$59.50	$59.50
Purchase #2	$125.97	9.676%	$138.1589	$138.16	$138.15	$138.20
Purchase #3	$208.89	8.323%	$226.2759	$226.28	$226.30	$226.30
Purchase #4	$176.60	11.280%	$196.5205	$196.52	$196.50	$196.50
Purchase #5	$63.49	5.683%	$67.0981	$67.10	$67.10	$67.10
Purchase #6	$153.41	9.147%	$167.4424	$167.44	$167.45	$167.40
Purchase #7	$100.25	10.409%	$110.685	$110.69	$110.70	$110.70
7 purchase totals =	$884.37		$965.6605	$965.67	$965.70	$965.70