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	$103.68	11.673%	$115.7826	$115.78	$115.80	$115.80
Purchase #2	$186.60	5.515%	$196.891	$196.89	$196.90	$196.90
Purchase #3	$37.83	9.697%	$41.4984	$41.50	$41.50	$41.50
Purchase #4	$161.72	13.147%	$182.9813	$182.98	$183.00	$183.00
Purchase #5	$72.49	12.293%	$81.4012	$81.40	$81.40	$81.40
Purchase #6	$55.66	6.244%	$59.1354	$59.14	$59.15	$59.10
Purchase #7	$221.80	4.542%	$231.8742	$231.87	$231.85	$231.90
7 purchase totals =	$839.78		$909.5641	$909.56	$909.60	$909.60