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	$22.33	12.799%	$25.188	$25.19	$25.20	$25.20
Purchase #2	$20.35	5.519%	$21.4731	$21.47	$21.45	$21.50
Purchase #3	$71.98	8.615%	$78.1811	$78.18	$78.20	$78.20
Purchase #4	$142.34	5.537%	$150.2214	$150.22	$150.20	$150.20
Purchase #5	$91.61	9.361%	$100.1856	$100.19	$100.20	$100.20
Purchase #6	$14.90	7.797%	$16.0618	$16.06	$16.05	$16.10
Purchase #7	$127.55	10.120%	$140.4581	$140.46	$140.45	$140.50
7 purchase totals =	$491.06		$531.7691	$531.77	$531.75	$531.90