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	$85.63	5.606%	$90.4304	$90.43	$90.45	$90.40
Purchase #2	$49.64	4.608%	$51.9274	$51.93	$51.95	$51.90
Purchase #3	$9.34	13.148%	$10.568	$10.57	$10.55	$10.60
Purchase #4	$154.69	5.334%	$162.9412	$162.94	$162.95	$162.90
Purchase #5	$113.58	13.742%	$129.1882	$129.19	$129.20	$129.20
Purchase #6	$116.83	12.283%	$131.1802	$131.18	$131.20	$131.20
Purchase #7	$38.48	10.455%	$42.5031	$42.50	$42.50	$42.50
7 purchase totals =	$568.19		$618.7385	$618.74	$618.80	$618.70