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	$215.34	3.301%	$222.4484	$222.45	$222.45	$222.40
Purchase #2	$18.71	13.175%	$21.175	$21.18	$21.20	$21.20
Purchase #3	$141.50	3.121%	$145.9162	$145.92	$145.90	$145.90
Purchase #4	$92.53	3.177%	$95.4697	$95.47	$95.45	$95.50
Purchase #5	$161.89	7.788%	$174.498	$174.50	$174.50	$174.50
Purchase #6	$70.87	10.237%	$78.125	$78.13	$78.15	$78.10
Purchase #7	$79.55	8.304%	$86.1558	$86.16	$86.15	$86.20
7 purchase totals =	$780.39		$823.7881	$823.81	$823.80	$823.80