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	$243.59	8.747%	$264.8968	$264.90	$264.90	$264.90
Purchase #2	$14.43	7.661%	$15.5355	$15.54	$15.55	$15.50
Purchase #3	$144.82	3.805%	$150.3304	$150.33	$150.35	$150.30
Purchase #4	$190.98	11.381%	$212.7154	$212.72	$212.70	$212.70
Purchase #5	$143.83	6.520%	$153.2077	$153.21	$153.20	$153.20
Purchase #6	$102.76	8.132%	$111.1164	$111.12	$111.10	$111.10
Purchase #7	$78.97	13.795%	$89.8639	$89.86	$89.85	$89.90
7 purchase totals =	$919.38		$997.6661	$997.68	$997.65	$997.60