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	$126.85	9.836%	$139.327	$139.33	$139.35	$139.30
Purchase #2	$224.93	13.691%	$255.7252	$255.73	$255.75	$255.70
Purchase #3	$44.60	8.468%	$48.3767	$48.38	$48.40	$48.40
Purchase #4	$142.34	7.137%	$152.4988	$152.50	$152.50	$152.50
Purchase #5	$72.83	7.245%	$78.1065	$78.11	$78.10	$78.10
Purchase #6	$62.33	3.440%	$64.4742	$64.47	$64.45	$64.50
Purchase #7	$190.87	5.710%	$201.7687	$201.77	$201.75	$201.80
7 purchase totals =	$864.75		$940.2771	$940.29	$940.30	$940.30