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	$72.99	7.140%	$78.2015	$78.20	$78.20	$78.20
Purchase #2	$36.62	13.645%	$41.6168	$41.62	$41.60	$41.60
Purchase #3	$138.60	3.650%	$143.6589	$143.66	$143.65	$143.70
Purchase #4	$201.66	13.639%	$229.1644	$229.16	$229.15	$229.20
Purchase #5	$149.97	9.590%	$164.3521	$164.35	$164.35	$164.40
Purchase #6	$150.73	3.841%	$156.5195	$156.52	$156.50	$156.50
Purchase #7	$175.92	5.665%	$185.8859	$185.89	$185.90	$185.90
7 purchase totals =	$926.49		$999.3991	$999.40	$999.35	$999.50