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	$246.91	13.652%	$280.6182	$280.62	$280.60	$280.60
Purchase #2	$236.80	4.188%	$246.7172	$246.72	$246.70	$246.70
Purchase #3	$92.36	7.103%	$98.9203	$98.92	$98.90	$98.90
Purchase #4	$17.58	5.498%	$18.5465	$18.55	$18.55	$18.50
Purchase #5	$101.47	9.732%	$111.3451	$111.35	$111.35	$111.30
Purchase #6	$196.33	6.281%	$208.6615	$208.66	$208.65	$208.70
Purchase #7	$165.30	11.196%	$183.807	$183.81	$183.80	$183.80
7 purchase totals =	$1,056.75		$1,148.6158	$1,148.63	$1,148.55	$1,148.50