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	$215.26	11.619%	$240.2711	$240.27	$240.25	$240.30
Purchase #2	$142.66	6.553%	$152.0085	$152.01	$152.00	$152.00
Purchase #3	$171.90	9.611%	$188.4213	$188.42	$188.40	$188.40
Purchase #4	$35.85	7.308%	$38.4699	$38.47	$38.45	$38.50
Purchase #5	$197.91	12.621%	$222.8882	$222.89	$222.90	$222.90
Purchase #6	$247.88	12.602%	$279.1178	$279.12	$279.10	$279.10
Purchase #7	$156.29	5.319%	$164.6031	$164.60	$164.60	$164.60
7 purchase totals =	$1,167.75		$1,285.7799	$1,285.78	$1,285.70	$1,285.80