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	$74.65	5.543%	$78.7878	$78.79	$78.80	$78.80
Purchase #2	$173.77	9.265%	$189.8698	$189.87	$189.85	$189.90
Purchase #3	$151.28	11.426%	$168.5653	$168.57	$168.55	$168.60
Purchase #4	$155.70	12.787%	$175.6094	$175.61	$175.60	$175.60
Purchase #5	$182.85	7.474%	$196.5162	$196.52	$196.50	$196.50
Purchase #6	$61.92	12.178%	$69.4606	$69.46	$69.45	$69.50
Purchase #7	$200.70	4.873%	$210.4801	$210.48	$210.50	$210.50
7 purchase totals =	$1,000.87		$1,089.2892	$1,089.30	$1,089.25	$1,089.40