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	$37.99	8.719%	$41.3023	$41.30	$41.30	$41.30
Purchase #2	$40.53	4.847%	$42.4945	$42.49	$42.50	$42.50
Purchase #3	$92.66	5.642%	$97.8879	$97.89	$97.90	$97.90
Purchase #4	$42.86	12.619%	$48.2685	$48.27	$48.25	$48.30
Purchase #5	$155.54	9.109%	$169.7081	$169.71	$169.70	$169.70
Purchase #6	$141.77	8.712%	$154.121	$154.12	$154.10	$154.10
Purchase #7	$247.74	10.443%	$273.6115	$273.61	$273.60	$273.60
7 purchase totals =	$759.09		$827.3938	$827.39	$827.35	$827.40