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	$7.89	7.669%	$8.4951	$8.50	$8.50	$8.50
Purchase #2	$131.71	9.750%	$144.5517	$144.55	$144.55	$144.60
Purchase #3	$177.82	9.280%	$194.3217	$194.32	$194.30	$194.30
Purchase #4	$157.75	9.808%	$173.2221	$173.22	$173.20	$173.20
Purchase #5	$209.67	3.433%	$216.868	$216.87	$216.85	$216.90
Purchase #6	$170.73	3.301%	$176.3658	$176.37	$176.35	$176.40
Purchase #7	$189.92	3.253%	$196.0981	$196.10	$196.10	$196.10
7 purchase totals =	$1,045.49		$1,109.9225	$1,109.93	$1,109.85	$1,110.00