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	$124.45	5.655%	$131.4876	$131.49	$131.50	$131.50
Purchase #2	$57.32	7.630%	$61.6935	$61.69	$61.70	$61.70
Purchase #3	$116.91	10.632%	$129.3399	$129.34	$129.35	$129.30
Purchase #4	$94.94	9.780%	$104.2251	$104.23	$104.25	$104.20
Purchase #5	$70.58	10.730%	$78.1532	$78.15	$78.15	$78.20
Purchase #6	$200.36	11.847%	$224.0966	$224.10	$224.10	$224.10
Purchase #7	$143.66	12.195%	$161.1793	$161.18	$161.20	$161.20
7 purchase totals =	$808.22		$890.1752	$890.18	$890.25	$890.20