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	$111.37	13.182%	$126.0508	$126.05	$126.05	$126.10
Purchase #2	$135.45	11.393%	$150.8818	$150.88	$150.90	$150.90
Purchase #3	$96.95	8.784%	$105.4661	$105.47	$105.45	$105.50
Purchase #4	$168.76	10.177%	$185.9347	$185.93	$185.95	$185.90
Purchase #5	$21.50	13.286%	$24.3565	$24.36	$24.35	$24.40
Purchase #6	$28.91	3.599%	$29.9505	$29.95	$29.95	$30.00
Purchase #7	$177.96	7.787%	$191.8177	$191.82	$191.80	$191.80
7 purchase totals =	$740.90		$814.4581	$814.46	$814.45	$814.60