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	$66.76	5.142%	$70.1928	$70.19	$70.20	$70.20
Purchase #2	$47.82	5.119%	$50.2679	$50.27	$50.25	$50.30
Purchase #3	$143.61	6.726%	$153.2692	$153.27	$153.25	$153.30
Purchase #4	$179.72	12.549%	$202.2731	$202.27	$202.25	$202.30
Purchase #5	$70.55	10.858%	$78.2103	$78.21	$78.20	$78.20
Purchase #6	$35.51	12.367%	$39.9015	$39.90	$39.90	$39.90
Purchase #7	$201.60	10.152%	$222.0664	$222.07	$222.05	$222.10
7 purchase totals =	$745.57		$816.1812	$816.18	$816.10	$816.30