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	$185.31	13.228%	$209.8228	$209.82	$209.80	$209.80
Purchase #2	$36.78	12.162%	$41.2532	$41.25	$41.25	$41.30
Purchase #3	$158.50	6.502%	$168.8057	$168.81	$168.80	$168.80
Purchase #4	$79.36	9.339%	$86.7714	$86.77	$86.75	$86.80
Purchase #5	$21.97	11.470%	$24.49	$24.49	$24.50	$24.50
Purchase #6	$158.29	9.222%	$172.8875	$172.89	$172.90	$172.90
Purchase #7	$158.57	3.127%	$163.5285	$163.53	$163.55	$163.50
7 purchase totals =	$798.78		$867.5591	$867.56	$867.55	$867.60