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	$249.82	3.165%	$257.7268	$257.73	$257.75	$257.70
Purchase #2	$119.48	6.674%	$127.4541	$127.45	$127.45	$127.50
Purchase #3	$129.70	10.450%	$143.2537	$143.25	$143.25	$143.30
Purchase #4	$164.96	3.351%	$170.4878	$170.49	$170.50	$170.50
Purchase #5	$57.44	8.521%	$62.3345	$62.33	$62.35	$62.30
Purchase #6	$78.59	11.386%	$87.5383	$87.54	$87.55	$87.50
Purchase #7	$95.79	4.151%	$99.7662	$99.77	$99.75	$99.80
7 purchase totals =	$895.78		$948.5614	$948.56	$948.60	$948.60