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	$186.38	6.821%	$199.093	$199.09	$199.10	$199.10
Purchase #2	$124.75	9.441%	$136.5276	$136.53	$136.55	$136.50
Purchase #3	$97.25	3.283%	$100.4427	$100.44	$100.45	$100.40
Purchase #4	$143.82	4.441%	$150.207	$150.21	$150.20	$150.20
Purchase #5	$38.43	7.667%	$41.3764	$41.38	$41.40	$41.40
Purchase #6	$95.61	10.229%	$105.3899	$105.39	$105.40	$105.40
Purchase #7	$130.25	11.664%	$145.4424	$145.44	$145.45	$145.40
7 purchase totals =	$816.49		$878.4790	$878.48	$878.55	$878.40