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	$199.79	12.278%	$224.3202	$224.32	$224.30	$224.30
Purchase #2	$86.99	9.680%	$95.4106	$95.41	$95.40	$95.40
Purchase #3	$46.73	11.617%	$52.1586	$52.16	$52.15	$52.20
Purchase #4	$163.78	13.158%	$185.3302	$185.33	$185.35	$185.30
Purchase #5	$194.46	9.798%	$213.5132	$213.51	$213.50	$213.50
Purchase #6	$126.72	3.585%	$131.2629	$131.26	$131.25	$131.30
Purchase #7	$53.57	7.494%	$57.5845	$57.58	$57.60	$57.60
7 purchase totals =	$872.04		$959.5802	$959.57	$959.55	$959.60