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	$90.54	10.728%	$100.2531	$100.25	$100.25	$100.30
Purchase #2	$179.79	3.250%	$185.6332	$185.63	$185.65	$185.60
Purchase #3	$86.30	7.602%	$92.8605	$92.86	$92.85	$92.90
Purchase #4	$196.96	13.366%	$223.2857	$223.29	$223.30	$223.30
Purchase #5	$156.31	4.807%	$163.8238	$163.82	$163.80	$163.80
Purchase #6	$85.91	10.308%	$94.7656	$94.77	$94.75	$94.80
Purchase #7	$18.67	6.560%	$19.8948	$19.89	$19.90	$19.90
7 purchase totals =	$814.48		$880.5167	$880.51	$880.50	$880.60