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	$24.33	10.165%	$26.8031	$26.80	$26.80	$26.80
Purchase #2	$19.72	5.312%	$20.7675	$20.77	$20.75	$20.80
Purchase #3	$113.97	4.210%	$118.7681	$118.77	$118.75	$118.80
Purchase #4	$18.95	12.309%	$21.2826	$21.28	$21.30	$21.30
Purchase #5	$56.53	4.789%	$59.2372	$59.24	$59.25	$59.20
Purchase #6	$217.56	11.342%	$242.2357	$242.24	$242.25	$242.20
Purchase #7	$50.47	6.858%	$53.9312	$53.93	$53.95	$53.90
7 purchase totals =	$501.53		$543.0254	$543.03	$543.05	$543.00