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	$226.48	10.287%	$249.778	$249.78	$249.80	$249.80
Purchase #2	$163.33	7.102%	$174.9297	$174.93	$174.95	$174.90
Purchase #3	$241.78	4.211%	$251.9614	$251.96	$251.95	$252.00
Purchase #4	$99.83	9.765%	$109.5784	$109.58	$109.60	$109.60
Purchase #5	$219.79	5.275%	$231.3839	$231.38	$231.40	$231.40
Purchase #6	$174.78	12.211%	$196.1224	$196.12	$196.10	$196.10
Purchase #7	$101.53	4.782%	$106.3852	$106.39	$106.40	$106.40
7 purchase totals =	$1,227.52		$1,320.1390	$1,320.14	$1,320.20	$1,320.20