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	$186.78	12.474%	$210.0789	$210.08	$210.10	$210.10
Purchase #2	$203.92	10.407%	$225.142	$225.14	$225.15	$225.10
Purchase #3	$120.30	9.210%	$131.3796	$131.38	$131.40	$131.40
Purchase #4	$103.87	8.778%	$112.9877	$112.99	$113.00	$113.00
Purchase #5	$88.69	4.276%	$92.4824	$92.48	$92.50	$92.50
Purchase #6	$99.62	6.259%	$105.8552	$105.86	$105.85	$105.90
Purchase #7	$184.57	13.175%	$208.8871	$208.89	$208.90	$208.90
7 purchase totals =	$987.75		$1,086.8129	$1,086.82	$1,086.90	$1,086.90