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	$10.58	13.471%	$12.0052	$12.01	$12.00	$12.00
Purchase #2	$35.27	7.309%	$37.8479	$37.85	$37.85	$37.80
Purchase #3	$168.44	4.538%	$176.0838	$176.08	$176.10	$176.10
Purchase #4	$68.58	5.553%	$72.3882	$72.39	$72.40	$72.40
Purchase #5	$48.51	9.196%	$52.971	$52.97	$52.95	$53.00
Purchase #6	$72.54	10.168%	$79.9159	$79.92	$79.90	$79.90
Purchase #7	$249.84	3.464%	$258.4945	$258.49	$258.50	$258.50
7 purchase totals =	$653.76		$689.7065	$689.71	$689.70	$689.70