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	$95.43	9.558%	$104.5512	$104.55	$104.55	$104.60
Purchase #2	$229.71	13.323%	$260.3143	$260.31	$260.30	$260.30
Purchase #3	$20.84	3.709%	$21.613	$21.61	$21.60	$21.60
Purchase #4	$190.27	3.195%	$196.3491	$196.35	$196.35	$196.30
Purchase #5	$129.62	6.364%	$137.869	$137.87	$137.85	$137.90
Purchase #6	$37.36	9.132%	$40.7717	$40.77	$40.75	$40.80
Purchase #7	$71.50	9.509%	$78.2989	$78.30	$78.30	$78.30
7 purchase totals =	$774.73		$839.7672	$839.76	$839.70	$839.80