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	$131.69	5.168%	$138.4957	$138.50	$138.50	$138.50
Purchase #2	$153.33	9.170%	$167.3904	$167.39	$167.40	$167.40
Purchase #3	$77.80	11.567%	$86.7991	$86.80	$86.80	$86.80
Purchase #4	$27.59	10.784%	$30.5653	$30.57	$30.55	$30.60
Purchase #5	$22.82	8.630%	$24.7894	$24.79	$24.80	$24.80
Purchase #6	$205.76	4.758%	$215.5501	$215.55	$215.55	$215.60
Purchase #7	$79.85	12.519%	$89.8464	$89.85	$89.85	$89.80
7 purchase totals =	$698.84		$753.4364	$753.45	$753.45	$753.50