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	$249.30	3.325%	$257.5892	$257.59	$257.60	$257.60
Purchase #2	$169.87	11.658%	$189.6734	$189.67	$189.65	$189.70
Purchase #3	$200.86	9.443%	$219.8272	$219.83	$219.85	$219.80
Purchase #4	$163.54	13.546%	$185.6931	$185.69	$185.70	$185.70
Purchase #5	$71.85	3.811%	$74.5882	$74.59	$74.60	$74.60
Purchase #6	$67.69	5.669%	$71.5273	$71.53	$71.55	$71.50
Purchase #7	$91.79	7.227%	$98.4237	$98.42	$98.40	$98.40
7 purchase totals =	$1,014.90		$1,097.3221	$1,097.32	$1,097.35	$1,097.30