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	$103.65	7.549%	$111.4745	$111.47	$111.45	$111.50
Purchase #2	$113.88	8.418%	$123.4664	$123.47	$123.45	$123.50
Purchase #3	$237.84	13.732%	$270.5002	$270.50	$270.50	$270.50
Purchase #4	$131.47	6.467%	$139.9722	$139.97	$139.95	$140.00
Purchase #5	$128.26	6.760%	$136.9304	$136.93	$136.95	$136.90
Purchase #6	$86.25	12.858%	$97.34	$97.34	$97.35	$97.30
Purchase #7	$131.30	5.567%	$138.6095	$138.61	$138.60	$138.60
7 purchase totals =	$932.65		$1,018.2932	$1,018.29	$1,018.25	$1,018.30