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	$59.93	4.335%	$62.528	$62.53	$62.55	$62.50
Purchase #2	$107.58	6.380%	$114.4436	$114.44	$114.45	$114.40
Purchase #3	$20.39	12.239%	$22.8855	$22.89	$22.90	$22.90
Purchase #4	$119.58	10.320%	$131.9207	$131.92	$131.90	$131.90
Purchase #5	$248.71	9.278%	$271.7853	$271.79	$271.80	$271.80
Purchase #6	$188.72	11.542%	$210.5021	$210.50	$210.50	$210.50
Purchase #7	$5.89	3.299%	$6.0843	$6.08	$6.10	$6.10
7 purchase totals =	$750.80		$820.1495	$820.15	$820.20	$820.10