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	$27.63	6.585%	$29.4494	$29.45	$29.45	$29.40
Purchase #2	$22.39	7.369%	$24.0399	$24.04	$24.05	$24.00
Purchase #3	$126.30	3.747%	$131.0325	$131.03	$131.05	$131.00
Purchase #4	$178.43	10.229%	$196.6816	$196.68	$196.70	$196.70
Purchase #5	$66.46	8.818%	$72.3204	$72.32	$72.30	$72.30
Purchase #6	$79.90	9.494%	$87.4857	$87.49	$87.50	$87.50
Purchase #7	$42.60	6.802%	$45.4977	$45.50	$45.50	$45.50
7 purchase totals =	$543.71		$586.5072	$586.51	$586.55	$586.40