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	$131.94	5.674%	$139.4263	$139.43	$139.45	$139.40
Purchase #2	$169.83	9.271%	$185.5749	$185.57	$185.55	$185.60
Purchase #3	$228.59	3.776%	$237.2216	$237.22	$237.20	$237.20
Purchase #4	$35.69	12.584%	$40.1812	$40.18	$40.20	$40.20
Purchase #5	$39.92	9.820%	$43.8401	$43.84	$43.85	$43.80
Purchase #6	$98.85	10.490%	$109.2194	$109.22	$109.20	$109.20
Purchase #7	$100.62	8.387%	$109.059	$109.06	$109.05	$109.10
7 purchase totals =	$805.44		$864.5225	$864.52	$864.50	$864.50