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	$189.27	6.230%	$201.0615	$201.06	$201.05	$201.10
Purchase #2	$89.60	11.429%	$99.8404	$99.84	$99.85	$99.80
Purchase #3	$52.91	12.492%	$59.5195	$59.52	$59.50	$59.50
Purchase #4	$206.52	3.734%	$214.2315	$214.23	$214.25	$214.20
Purchase #5	$182.83	9.326%	$199.8807	$199.88	$199.90	$199.90
Purchase #6	$91.63	7.403%	$98.4134	$98.41	$98.40	$98.40
Purchase #7	$120.59	13.353%	$136.6924	$136.69	$136.70	$136.70
7 purchase totals =	$933.35		$1,009.6394	$1,009.63	$1,009.65	$1,009.60