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	$80.90	10.629%	$89.4989	$89.50	$89.50	$89.50
Purchase #2	$81.92	10.559%	$90.5699	$90.57	$90.55	$90.60
Purchase #3	$132.71	13.527%	$150.6617	$150.66	$150.65	$150.70
Purchase #4	$95.76	7.106%	$102.5647	$102.56	$102.55	$102.60
Purchase #5	$204.25	5.289%	$215.0528	$215.05	$215.05	$215.10
Purchase #6	$54.26	5.656%	$57.3289	$57.33	$57.35	$57.30
Purchase #7	$188.59	13.339%	$213.746	$213.75	$213.75	$213.70
7 purchase totals =	$838.39		$919.4229	$919.42	$919.40	$919.50