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	$225.76	6.399%	$240.2064	$240.21	$240.20	$240.20
Purchase #2	$145.73	4.633%	$152.4817	$152.48	$152.50	$152.50
Purchase #3	$122.91	13.671%	$139.713	$139.71	$139.70	$139.70
Purchase #4	$114.39	4.352%	$119.3683	$119.37	$119.35	$119.40
Purchase #5	$10.25	13.448%	$11.6284	$11.63	$11.65	$11.60
Purchase #6	$78.53	5.602%	$82.9293	$82.93	$82.95	$82.90
Purchase #7	$29.66	11.129%	$32.9609	$32.96	$32.95	$33.00
7 purchase totals =	$727.23		$779.2880	$779.29	$779.30	$779.30