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	$87.84	13.399%	$99.6097	$99.61	$99.60	$99.60
Purchase #2	$52.38	12.650%	$59.0061	$59.01	$59.00	$59.00
Purchase #3	$93.90	10.158%	$103.4384	$103.44	$103.45	$103.40
Purchase #4	$149.61	10.866%	$165.8666	$165.87	$165.85	$165.90
Purchase #5	$146.51	11.565%	$163.4539	$163.45	$163.45	$163.50
Purchase #6	$230.40	9.718%	$252.7903	$252.79	$252.80	$252.80
Purchase #7	$180.50	3.663%	$187.1117	$187.11	$187.10	$187.10
7 purchase totals =	$941.14		$1,031.2767	$1,031.28	$1,031.25	$1,031.30