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	$11.68	3.123%	$12.0448	$12.04	$12.05	$12.00
Purchase #2	$115.53	13.796%	$131.4685	$131.47	$131.45	$131.50
Purchase #3	$116.66	7.691%	$125.6323	$125.63	$125.65	$125.60
Purchase #4	$180.88	5.333%	$190.5263	$190.53	$190.55	$190.50
Purchase #5	$105.30	6.460%	$112.1024	$112.10	$112.10	$112.10
Purchase #6	$174.61	7.516%	$187.7337	$187.73	$187.75	$187.70
Purchase #7	$11.97	13.639%	$13.6026	$13.60	$13.60	$13.60
7 purchase totals =	$716.63		$773.1106	$773.10	$773.15	$773.00