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	$112.95	13.226%	$127.8888	$127.89	$127.90	$127.90
Purchase #2	$226.36	10.287%	$249.6457	$249.65	$249.65	$249.60
Purchase #3	$74.96	10.724%	$82.9987	$83.00	$83.00	$83.00
Purchase #4	$115.84	13.292%	$131.2375	$131.24	$131.25	$131.20
Purchase #5	$40.81	3.684%	$42.3134	$42.31	$42.30	$42.30
Purchase #6	$34.77	13.611%	$39.5025	$39.50	$39.50	$39.50
Purchase #7	$134.65	6.237%	$143.0481	$143.05	$143.05	$143.00
7 purchase totals =	$740.34		$816.6347	$816.64	$816.65	$816.50