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	$103.83	12.644%	$116.9583	$116.96	$116.95	$117.00
Purchase #2	$72.80	13.757%	$82.8151	$82.82	$82.80	$82.80
Purchase #3	$15.48	5.823%	$16.3814	$16.38	$16.40	$16.40
Purchase #4	$44.48	13.858%	$50.644	$50.64	$50.65	$50.60
Purchase #5	$231.76	12.676%	$261.1379	$261.14	$261.15	$261.10
Purchase #6	$82.33	8.632%	$89.4367	$89.44	$89.45	$89.40
Purchase #7	$50.44	11.773%	$56.3783	$56.38	$56.40	$56.40
7 purchase totals =	$601.12		$673.7517	$673.76	$673.80	$673.70