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	$83.57	8.424%	$90.6099	$90.61	$90.60	$90.60
Purchase #2	$144.74	3.735%	$150.146	$150.15	$150.15	$150.10
Purchase #3	$210.61	5.423%	$222.0314	$222.03	$222.05	$222.00
Purchase #4	$5.27	11.252%	$5.863	$5.86	$5.85	$5.90
Purchase #5	$66.32	10.196%	$73.082	$73.08	$73.10	$73.10
Purchase #6	$133.30	8.345%	$144.4239	$144.42	$144.40	$144.40
Purchase #7	$132.91	5.476%	$140.1882	$140.19	$140.20	$140.20
7 purchase totals =	$776.72		$826.3444	$826.34	$826.35	$826.30