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	$235.76	12.440%	$265.0885	$265.09	$265.10	$265.10
Purchase #2	$31.47	9.723%	$34.5298	$34.53	$34.55	$34.50
Purchase #3	$41.90	3.796%	$43.4905	$43.49	$43.50	$43.50
Purchase #4	$143.64	6.558%	$153.0599	$153.06	$153.05	$153.10
Purchase #5	$129.70	10.523%	$143.3483	$143.35	$143.35	$143.30
Purchase #6	$90.83	5.127%	$95.4869	$95.49	$95.50	$95.50
Purchase #7	$219.61	8.422%	$238.1056	$238.11	$238.10	$238.10
7 purchase totals =	$892.91		$973.1095	$973.12	$973.15	$973.10