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	$50.31	12.465%	$56.5811	$56.58	$56.60	$56.60
Purchase #2	$54.64	9.712%	$59.9466	$59.95	$59.95	$59.90
Purchase #3	$208.74	6.506%	$222.3206	$222.32	$222.30	$222.30
Purchase #4	$14.69	11.135%	$16.3257	$16.33	$16.35	$16.30
Purchase #5	$213.96	4.699%	$224.014	$224.01	$224.00	$224.00
Purchase #6	$176.26	4.149%	$183.573	$183.57	$183.55	$183.60
Purchase #7	$89.93	3.229%	$92.8338	$92.83	$92.85	$92.80
7 purchase totals =	$808.53		$855.5948	$855.59	$855.60	$855.50