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	$151.27	5.167%	$159.0861	$159.09	$159.10	$159.10
Purchase #2	$131.71	9.793%	$144.6084	$144.61	$144.60	$144.60
Purchase #3	$93.61	3.105%	$96.5166	$96.52	$96.50	$96.50
Purchase #4	$22.77	3.149%	$23.487	$23.49	$23.50	$23.50
Purchase #5	$179.34	9.401%	$196.1998	$196.20	$196.20	$196.20
Purchase #6	$88.63	12.264%	$99.4996	$99.50	$99.50	$99.50
Purchase #7	$156.44	9.448%	$171.2205	$171.22	$171.20	$171.20
7 purchase totals =	$823.77		$890.6180	$890.63	$890.60	$890.60