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	$52.77	12.705%	$59.4744	$59.47	$59.45	$59.50
Purchase #2	$86.72	13.165%	$98.1367	$98.14	$98.15	$98.10
Purchase #3	$89.45	8.572%	$97.1177	$97.12	$97.10	$97.10
Purchase #4	$101.41	8.231%	$109.7571	$109.76	$109.75	$109.80
Purchase #5	$123.30	10.426%	$136.1553	$136.16	$136.15	$136.20
Purchase #6	$208.47	8.405%	$225.9919	$225.99	$226.00	$226.00
Purchase #7	$101.73	3.422%	$105.2112	$105.21	$105.20	$105.20
7 purchase totals =	$763.85		$831.8443	$831.85	$831.80	$831.90