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	$91.39	9.836%	$100.3791	$100.38	$100.40	$100.40
Purchase #2	$199.72	10.541%	$220.7725	$220.77	$220.75	$220.80
Purchase #3	$191.25	13.146%	$216.3917	$216.39	$216.40	$216.40
Purchase #4	$41.96	3.712%	$43.5176	$43.52	$43.50	$43.50
Purchase #5	$156.44	6.841%	$167.1421	$167.14	$167.15	$167.10
Purchase #6	$107.71	5.739%	$113.8915	$113.89	$113.90	$113.90
Purchase #7	$144.78	10.235%	$159.5982	$159.60	$159.60	$159.60
7 purchase totals =	$933.25		$1,021.6927	$1,021.69	$1,021.70	$1,021.70