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	$194.38	3.147%	$200.4971	$200.50	$200.50	$200.50
Purchase #2	$132.37	5.325%	$139.4187	$139.42	$139.40	$139.40
Purchase #3	$241.25	3.450%	$249.5731	$249.57	$249.55	$249.60
Purchase #4	$72.48	13.486%	$82.2547	$82.25	$82.25	$82.30
Purchase #5	$184.27	11.866%	$206.1355	$206.14	$206.15	$206.10
Purchase #6	$130.32	8.290%	$141.1235	$141.12	$141.10	$141.10
Purchase #7	$210.38	5.311%	$221.5533	$221.55	$221.55	$221.60
7 purchase totals =	$1,165.45		$1,240.5559	$1,240.55	$1,240.50	$1,240.60