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	$102.50	5.402%	$108.0371	$108.04	$108.05	$108.00
Purchase #2	$42.50	10.810%	$47.0943	$47.09	$47.10	$47.10
Purchase #3	$73.90	11.744%	$82.5788	$82.58	$82.60	$82.60
Purchase #4	$27.53	11.117%	$30.5905	$30.59	$30.60	$30.60
Purchase #5	$90.52	5.602%	$95.5909	$95.59	$95.60	$95.60
Purchase #6	$29.69	4.591%	$31.0531	$31.05	$31.05	$31.10
Purchase #7	$236.45	3.830%	$245.506	$245.51	$245.50	$245.50
7 purchase totals =	$603.09		$640.4507	$640.45	$640.50	$640.50