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	$137.53	4.584%	$143.8344	$143.83	$143.85	$143.80
Purchase #2	$131.37	5.856%	$139.063	$139.06	$139.05	$139.10
Purchase #3	$184.87	12.732%	$208.4076	$208.41	$208.40	$208.40
Purchase #4	$142.51	5.709%	$150.6459	$150.65	$150.65	$150.60
Purchase #5	$111.38	9.700%	$122.1839	$122.18	$122.20	$122.20
Purchase #6	$171.57	10.208%	$189.0839	$189.08	$189.10	$189.10
Purchase #7	$242.36	11.112%	$269.291	$269.29	$269.30	$269.30
7 purchase totals =	$1,121.59		$1,222.5097	$1,222.50	$1,222.55	$1,222.50