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	$23.38	7.389%	$25.1075	$25.11	$25.10	$25.10
Purchase #2	$92.82	12.113%	$104.0633	$104.06	$104.05	$104.10
Purchase #3	$132.51	5.316%	$139.5542	$139.55	$139.55	$139.60
Purchase #4	$23.37	7.265%	$25.0678	$25.07	$25.05	$25.10
Purchase #5	$145.88	4.838%	$152.9377	$152.94	$152.95	$152.90
Purchase #6	$130.99	10.824%	$145.1684	$145.17	$145.15	$145.20
Purchase #7	$218.87	11.245%	$243.4819	$243.48	$243.50	$243.50
7 purchase totals =	$767.82		$835.3808	$835.38	$835.35	$835.50